Effect of filarial antigen treatment on glucose metabolism and insulin sensitivity in Type-2 diabetic mice models.
Filariasis mediated immunomodulation against metabolic diseases is a recently identified novel phenomenon. There seems to be an inverse relationship between filarial infections and type-2 diabetes. Rapid elimination of filarial diseases, due to mass drug administration has somehow fueled the sudden and rampant increase in type-2 diabetes, at least in certain tropical countries, like India and Indonesia. Filarial infections are in a way unique, since they bring about immunomodulation, in contrast to inflammation which is triggered by viral and bacterial infections. This dampens immunity and confers better survival for the pathogen. However, this also attenuates chronic inflammation and insulin resistance and thereby confers protection against type-2 diabetes. This chapter elucidates the various immune mechanisms involved in immunomodulation against insulin resistance and type-2 diabetes induced by helminth infection.
- Insulin Resistance
- Helminth infections
- Metabolic diseases
1.1 What is metainflammation?
Chronic inflammation has long been recognized as a major etiological factor for metabolic diseases . The inflammation in metabolic diseases is chronic, low grade and non-antigen-specific but differs from one condition to other . This is different from those seen in infectious diseases and has been named “Metainflammation”. Meta inflammation leads to insulin resistance (IR) wherein the target organs of insulin become resistant to insulin action . IR has now been identified as a major etiological factor for a variety of metabolic diseases, apart from obesity and Type-2 diabetes (T2DM) . Meta inflammation typically starts as an organ-specific inflammation affecting the major target organs of insulin namely adipose tissue, skeletal muscles and liver . With disease progression, it becomes more systemic and starts affecting the blood vessels leading to endothelial dysfunction called vasculopathy . The exact cause of inflammation in IR is not clearly known even though dietary, genetic and environmental factors have been implicated .
1.2 Helminth infection as an immunomodulation strategy
Infections serve as an important source of inflammation especially in tropical countries and can serve as a link between infections and metabolic diseases . The link between infections and metabolic diseases is less well explored and in recent years has gained tremendous interest . Changes in the lifestyle of people living in industrialized countries have led to a decrease in the infectious burden and an increase in the prevalence of allergic and autoimmune diseases . The leading idea is that some infectious agents – notably those that co-evolved with us – are able to protect us against a large spectrum of immune-related disorders . The strongest evidence for a causal relationship between the decline of infectious diseases and the increase in immunological disorders originates from animal models and a number of clinical studies, suggesting the beneficial effect of infectious agents or their components known as immunomodulators . Immunomodulators are drugs or molecules (Thalidomide. Macrolide antibiotics, and curcumin) that modify the dangerous immune response to prevent the inflammatory damage, while leaving the protective immune response intact . It is speculated that infections as such are important in keeping the immunoregulatory network active and, in the absence of such infections, the immune system gets hyperactivated, resulting in allergies and autoimmunity . In this regard, the helminth infections need a special mention since they were found to be alleviating numerous autoimmune disorders like atopic disorders, systemic lupus erythematosus, multiple sclerosis, sepsis, inflammatory bowel diseases .
Not all infections promote inflammation. While in general, viral and bacterial diseases induce inflammation, helminth infections are largely immunosuppressive in nature . The link between fungal and protozoan diseases, with systemic inflammation, is not known. In general, infections which promote inflammation are thought to augment metabolic diseases while those which dampen inflammation by immunomodulation can confer protection against metabolic diseases . Previously, we have shown a decreased prevalence of filarial infection (not disease) among both T1DM  and T2DM subjects . Further, serum cytokine profiling revealed the downregulation of Interleukin-6 (IL-6), Tumour Necrosis Factor-alpha (TNF-α) and Granulocyte-Macrophage-Colony Stimulating Factor (GM-CSF) and upregulation of Tumour Growth Factor-Beta (TGF-β) in filarial positive, compared to filarial negative diabetic subjects . Interestingly, the immunomodulatory effect of helminth infection was seen only inT1DM and T2DM subjects but not among the coronary artery disease (CAD) patients . Even though these were cross-sectional studies, they indicate probable immune-mediated protection against both T1DM and T2DM by prior filarial infection. This also indicates some degree of overlap in the disease pathology between these two seemingly different forms of diabetes, which the helminth infection is able to target [3, 11]. If this is true, the decreasing incidence of filariasis (due to mass drug administration programs) which is being carried globally, can fuel diabetic pandemic in future [3, 11]. Thus, childhood infection can either have a beneficial or harmful role in determining the susceptibility to T2DM depending upon the nature of immune training-induced [3, 11].
2. Role of innate immune cells in insulin resistance and immunomodulation
Traditionally monocytes/macrophages, dendritic cells, Natural killer (NK) cells and granulocytes (neutrophils, eosinophils and basophils) together form the cellular arm of innate immunity, since they recognize the pathogen and damage-associated molecular patterns (PAMPs and DAMPs) . T and B lymphocytes together form the cellular arm of the adaptive immunity, since they recognize antigens/epitopes and have immunological memory . During an immune response, cells of innate immunity recognize PAMPs and DAMPs through various innate immune receptors like Toll-like Receptors (TLRs), NOD-Like Receptors (NLRs), RIG-1 Like Receptors (RLRs) and C-Type Lectin Like Receptors (CLRs), etc. and get activated. Most of these cells take up the cargo, process them and present them to the T cells within the context of MHC . B cells on the other hand take up antigens by antibody-mediated endocytosis, process them and present them to the T cells . The T cells which recognize these MHC: epitope complexes through their T Cell Receptors (TCRs), get activated and secrete cytokines and chemokines . These cytokines and chemokines in turn activate and attract more number of antigen-presenting cells (APCs), completing the positive feedback loop . Thus, antigen processing and presentation and subsequent secretion of cytokines and chemokines establish the cross-talks between innate and adaptive immune responses, which finally determine the magnitude and nature of the immune response . Next, we will look at the role played by specific cell-types in IR and immunomodulation.
2.1 Macrophages in insulin resistance and immunomodulation
Out of several immune cell types, macrophages were the earliest to be associated with IR . Macrophages are phagocytic cells that serve as the first line of defence mechanism against infections . They are of two types: M1 (classically activated) and M2 (alternatively activated), which differ in their cytokine secretion and functions . The infiltration of macrophages into adipose tissue under conditions of obesity-associated IR was reported as early as 1976 . Classically activated or CD11c+CD206− M1 macrophages were found to be elevated in visceral adipose tissue (VAT) of diet-induced obese (DIO) mice which secrete increased levels of pro-inflammatory cytokines like TNF-α, IL-1β and IL-6 (Figure 1) . Transcriptional profiling of adipose tissue from leptin knock-out mice revealed the upregulation of 1,304 genes which showed a strong correlation with the body mass index. Of the top 100 genes which were differentially expressed, 30% were specific for macrophages . Resident macrophages in lean mice expressed Macrophage Galactose-binding C-type lectin (MGL-1) along with other genes associated with M2 macrophages (Ym1+, CCR2−, Arg-1+ and IL-10, 15, 16]. With diet-induced obesity, a new population of Ym1−, MGL-1−, CCR2+, iNOS+ M1 macrophages were recruited which cluster around the necrotic adipocytes forming crown-like structures. While the M1 macrophages are associated with IR, M2 is more associated with insulin sensitivity (Figure 1) [15, 16, 17]. In general, peripheral macrophages in newly diagnosed diabetic patients are hyporesponsive to inflammatory signals due to the downregulation of TLRs . In contrast, macrophages from chronic diabetic patients show chronic activation due to constitutive upregulation of B7–1 molecules .
With respect to helminth infection, despite the central role played by lymphocytes and dendritic cells, the role played by macrophages in both pathology and protection cannot be undermined . Helminth products are known to polarize macrophages into M2 phenotype which orchestrate fibrosis and wound healing . Helminth infected macrophages are also termed as nematode-elicited macrophages that express a peculiar M2 phenotype . The master cytokines involved in M2 polarization are IL-4 and IL-13. The macrophages which are polarized by helminth infection express YM1, YM2, Resistin-Like Molecule alpha (RELMα) and other markers of M2 phenotype and produce IL-10 . Diet-induced obese mice treated with
|S. No||Filarial antigen||Organism/species||Disease condition||Immune cells involved||Mechanisms||Outcome||Ref.|
|1||C57BL/6 J DIO mice and C57BL/6 J DEREG mice||Diet induced obesity and glucose intolerance||Eosinophils, macrophages, innate lymphoid cells||Increased number of eosinophils, M2 macrophages, ILC-2 and Tregs in AT||Increased insulin sensitivity and glucose tolerance|||
|2||C57BL/6 J mice||Diet induced obesity and glucose intolerance||Macrophages||Increased M2 macrophages and increased expression of IL-13.||Reduced body weight and improved glucose metabolism|||
|3||BALB/c mice||STZ induced T1D||Antibodies||Increased IgE levels and sub-isotype switch of anti-insulin antibodies from IgG2a to IgG.||Improvement in glucose metabolism|||
|4||Filarial proteins rWbL2(recombinant ||Female Balb/c mice||STZ induced T1D||Antibodies||Inhibition of TNF-α and IFN-γ secretion and augmentation of IL-4, IL-5 and IL-10 secretion.Production of insulin specific IgG1 and antigen-specific IgE antibodies||Improvement in glucose metabolism|||
|5||rDiAg (Recombinant ||NOD/shi female mice||Autoimmune T1D||Antibodies||Reduced level of anti insulin autoantibodies. Th1 to Th2 shify. Elevated IgE levels||Prevention of insulitis|||
2.2 Dendritic cells in insulin resistance and immunomodulation
While macrophages are major phagocytic cells, Dendritic cells (DCs) are the major antigen-presenting cells that play a crucial role in linking innate and adaptive immunity. DCs can interact with both T cells and B cells. Animal studies looking at the role of DCs in IR are limited. The CD11c+ myeloid DCs were significantly increased in the adipose tissue of obese mice . This suggests that DCs might be involved in T cell polarization and activation of macrophages thereby playing an important role in adipose inflammation and IR . In the adipose tissue of obese mice, there was a substantial increase in the percentage of DCs which was associated with crown-like structures . Mice lacking DCs (Flt3−/−) had reduced number of adipose and liver macrophage content, whereas DC replacement in DC-null mice increased liver and adipose macrophage infiltration and IR . Both myeloid DCs and plasmacytoid DCs from chronic diabetic patients show upregulation of lineage markers due to high levels of circulating GM-CSF .
In helminth infections, DCs are arrested in an immature state characterized by an absence/moderate expression of co-stimulatory molecules along with reduced pro-inflammatory cytokine secretion . This feature might presumably induce the development of a Th2 immune response . While Toll-Like Receptor-mediated activation brings about DC maturation in general, helminth products have evolved alternate pathways of activation which can induce an anti-inflammatory response . Helminth antigen treated dendritic cells produced increased levels of IL-4 and IL-10 . Also, human monocyte-derived dendritic cells (mhDCs) when infected with live
2.3 Neutrophils in insulin resistance and immunomodulation
Neutrophils are microphages which are short-lived phagocytic cells that remove and destroy invading microorganisms and also cellular debris [38, 39]. In diet-induced obese mice, increased infiltration of neutrophil into adipose tissue was reported during weight gain and was associated with IR. In addition to host defence, neutrophil-derived serine proteases, such as neutrophil elastase, have been implicated in sterile inflammation . Treatment of hepatocytes with neutrophil elastase-induced IR (by IRS-1 degradation) while deletion of neutrophil elastase in obese mice restored insulin sensitivity . Taken together, neutrophils can be added to the extensive repertoire of immune cells that participate in inflammation-induced IR.
Compared to macrophages the role played by neutrophils in helminth infection is well studied . In recent times, like macrophages, neutrophils were shown to get polarized either towards classically activated (N1) or alternatively activated (N2) phenotypes, following bacterial infections . Whether such polarization takes place during helminth infections is not clearly known. Neutrophils were found to provide resistance to
2.4 Eosinophils in insulin resistance and immunomodulation
Eosinophils are generally associated with allergic responses as seen in parasitic infections . While IL-5 serves as the main growth factor for eosinophil development, eotaxins (CCL11, CLL24 and CCL26) serve as its major chemotactic factors . Activation of eosinophils results in its degranulation on to the target cells . They carry eosinophilic granules which are rich in cytotoxic cationic proteins including major basic protein (MBP), eosinophil peroxidase (EPO), eosinophilic cationic protein (ECP) and eosinophil-derived neurotoxin (EDN) . Adipose tissue eosinophils are needed for metabolic homeostasis and are involved in the maintenance of alternatively activated macrophages (AAMs) (Figure 1) . They serve as the major source of IL-4 which polarizes the macrophages into the M2 phenotype. Absence of eosinophils can lead to adiposity and systemic IR in obese mice . In these animals, IL-5 deficiency leads to loss of eosinophil accumulation in the adipose and increased IR .
Clinically, helminth infections are the most common cause of persistent eosinophilia, wherein they play a vital role in parasitic killing and elimination . Ligation of parasite-specific Ig to Fc receptors or direct binding of helminth products to TLRs leads to eosinophil activation and degranulation . Activated eosinophils bring about worm expulsion in two ways: 1. Direct killing of the worm by depositing cytotoxic granules along with reactive oxygen species on to the worm membrane and 2. Expulsion/encystment of the dead worm, by coordinating with other immune and non-immune cells . However, recent evidence has indicated eosinophil activation during helminths infection is an immune evasive strategy favouring the parasite . Eosinophils may influence the immune response in a manner that would sustain chronic infection and ensure worm survival . Recently, in a high-fat diet mice model, animals infected with
2.5 Basophils and mast cells in insulin resistance and immunomodulation
Basophils and mast cells are known for their involvement in allergies and airway inflammation . Both cell lineages share a common ancestry: while basophils circulate; mast cells remain resident in tissues under normal conditions [52, 53]. As like other immune cells, recent studies have implicated them in glucose homeostasis and adipogenesis . VAT from obese mice as well as humans contained a significant amount of mast cells . Mast cell-deficient mice showed better glucose homeostasis with increased metabolic rate . Leptin deficient Ob/Ob mice have an increased mast cell content in their adipose tissue and were found to secrete an increased amount of TNF-α .
Like eosinophils, basophils also serve in the first line of defence mechanism against helminth infection . However recently, this concept has been challenged for certain helminth infections . The cross-linking of surface IgE on basophils by helminth antigens induced IL-4 secretion . Thus, the anti-inflammatory Th-2 response is augmented by basophils and mast cells . During helminth infections, eosinophils, neutrophils and basophils directly participate in the parasite killing and expulsion . Basophil deficient mice, infected with L3 larvae of
2.6 NK and NKT cells in insulin resistance and immunomodulation
Natural killer (NK) cells are an important component of the innate immune response to viral infections and tumours . They have the ability to provide an early source of both innate (IL-6 and TNF-α) and adaptive (IFN-γ, IL-4, IL-5 and IL-13) immune cytokines and can also lyse the target cells through perforin-granzyme-mediated cytolytic pathway . Natural Killer T (NKT) cells are sub-population of lymphocytes that serve as a link between the innate and adaptive immunity . They are a heterogeneous group of lymphocytes that share the properties of both T cells and NK cells. Many of these cells recognize self and foreign lipids and glycolipids bound to the non-polymorphic CD1d molecule . Very little is known about the role played by NK and NKT cells in metabolic homeostasis . VAT obtained from obese subjects was found to have an increased frequency of IFN-γ expressing NK cells . The role of iNKT cells in the regulation of metabolism is just emerging. Previously, it was found that adipose tissues and liver of both mice and humans contain a population of iNKT cells, which decreased with increasing adiposity and IR (Figure 2) . In fact, this coincides with the infiltration of macrophages and T cells into the adipose tissue.
Compared to other cell types, the role played by NK cells in helminth mediated immunomodulation is intriguing. NK cells were found to express IL-4 and IL-13 in response to microfilaremia but not L3 infection . The early activation of NK cells led to apoptosis in response to live L3 exposure, but not to live microfilaremia infection . Impairment of NK cell function had a profound effect on worm burden and delays the clearance of the parasite. Infection of BALB/c mice with
2.7 Other innate immune cells in insulin resistance and immunomodulation
Myeloid-Derived Suppressor Cells (MDSCs) are heterogenous immature myeloid cells which were first discovered in the tumour stroma wherein they were found to suppress anti-tumour immune response . Recently, MDSCs were shown to alleviate insulin resistance and confer protection against diabetes . Adoptive transfer of MDSC cells into HFD mice showed better glucose tolerance . Loss of these cells in obese animals aggravated IR . Within the adipose tissue milieu, these cells were found to suppress Th1 activation . During helminth infection, anti-proliferative MDSCs emerge which inhibit T cell proliferation using eicosanoids generated through 12/15 lipoxygenase pathway . Similarly,
Nuocytes or Innate lymphoid cells (ILC) are recently discovered innate lymphoid cells capable of augmenting other immune cells like helper T cells . ILCs are primarily tissue-resident lymphocytes, found in both lymphoid (immune-associated), and non-lymphoid tissues, and rarely in the peripheral blood (<1%) [77, 78]. They are particularly abundant at mucosal surfaces controlling mucosal immunity and homeostasis [77, 79]. They differ from other immune cells by the absence of regular lymphoid morphology, TCR and BCR rearranged, and expression of myeloid-specific CD markers . Based on the difference in developmental pathways, phenotype, and cytokine secretion, in 2013, ILCs were divided into three groups: 1. ILC-1 cells upon priming with IL-12, IL-15 and IL-18 secrete IFN-γ and TNF-α; 2. ILC-2 cells upon priming with TSLP, IL-25 and IL-33 a secrete IL-4, IL-5 and IL-13; 3. ILC-3 cells upon priming with IL-1β, IL-23 and IL-6, secrete IL-17 and IL-22 . ILC-1 recruitment into the adipose tissue is directly linked to fat accumulation and exacerbates IR , while ILC-2 cells are involved in browning of visceral adipose tissue . During helminth infection, the early source of IL-13 was from nuocytes, through IL-25 and IL-33 dependant priming . Administration of
3. Adaptive immune cells in insulin resistance and immunomodulation
The adaptive immune cells include T cells and B cells which play an important role in both IR and immunomodulation.
3.1 T-helper cells in insulin resistance and immunomodulation
T cells are lymphocytes which mature from the thymus (and hence the name) and are the major components of the adaptive immune system . They perform three major functions: 1. Helper T cells (Th) activate B cells, macrophages, DCs, other T cells and other immune cells, 2. Cytotoxic T cells (Tc) directly kill tumour cells and pathogen-infected cells and 3. Regulatory T cells (Tregs) maintain immune homeostasis . The Th cells are distinguished by their CD4+ phenotype and are further classified based on their cytokine profile as 1.Th1 (IFN-γ, IL-2, and TNF-β), Th2 (IL-4, IL-5 and IL-13), 3. Th17 (IL-17 and IL-17F), 4.Th9 (IL-9 and IL-10), 5.Th22 (IL-22), etc. . T cells in coordination with macrophages and DCs fuel VAT inflammation . Both pro-inflammatory cytotoxic T cells (CTLs) and interferon-γ (IFN-γ)-producing Th-1 cells contribute to inflammation (Figure 2) . On the contrary, VAT-resident Tregs and Th2 cells tend to suppress inflammation (Figure 2) . Obese IFN-γ-knockout animals, compared with obese wild-type mice, showed modest improvements in insulin sensitivity, decreased adipocyte size, and an M2-macrophage phenotype and cytokine expression . Genetic ablation of IL-13 in mice resulted in hyperglycemia, which progressed to hepatic IR and systemic metabolic dysfunction . However, studies conducted in our lab on serum cytokine profiles in subjects with metabolic syndrome (MS) showed a mixed Th1-Th2 response with increased levels of IL-12, IFN-γ, IL-4, IL-5 and IL-13 in the serum of subjects with metabolic syndrome (a precondition of diabetes, if not already present) . The role of recently discovered Th17 in VAT inflammation is still an enigma. Some studies have shown strong pro-inflammatory phenotype for these cells inducing IR , while our study showed a decline in serum IL-17 levels in subjects with MS (Figure 2) . The Tregs in VAT has a unique function of maintaining immune-homeostasis and improving insulin signalling by PPAR-g activation . The role of other recently identified Th cell subtypes like Th22 and Th9 in IR is not clearly known. In general, type-2 diabetic subjects show a mixed Th1-Th2 response which becomes more Th1 polarized as the diabetic subjects develop microvascular  and macrovascular complications . Serum IL-17 levels are generally low in patients with diabetic nephropathy .
T cell-mediated immune responses during filarial infection depend on the phase of the infection: 1.The acute phase is skewed towards Th2 (IL-4, IL-5 and IL-13) response, 2. The chronic phase is skewed towards “modified Th2 response”, with Tregs playing a more prominent compared to Th2 cells and 3. The third phase is chronic pathology phase, which is characterized by a drastic shift from “modified Th2” response to Th1/Th17 (IFN-γ, IL-2 and IL-17) response, which happens only in those who develop lymphatic pathology . Thus, the differential immune response seen during various phases of the filarial infection is paralleled by the life cycle of the parasite: 1. Microfilaremic stage-predominant Th2 response, 2. Adult worm stage- modified Th2-Treg response and 3.Chronic pathology stage- Th1/Th17 response . Infection of HFD induced obese mice with
3.2 Cytotoxic T cells (CTLs) in insulin resistance and immunomodulation
Cytotoxic (CD8+) T cells are one of the effector cells in T-cell mediated immunity which directly kills the target cells (virus or bacteria-infected cells and tumour cells). CD8+ T cells were found to migrate into the adipose tissue much before the accumulation of macrophage in obese mice . IFN-γ produced by CTLs promotes the recruitment and polarization of M1 macrophages (Figure 1) . This results in adipose tissue inflammation and IR . In the obese mice, increased infiltration of CTLs into the adipose tissue around 22nd week after the initiation of a high-fat diet was seen . Antibody-mediated or genetic depletion of CTLs lowered macrophage infiltration and adipose inflammation, ameliorating IR .
When compared to T-helper cells, the amount of literature available on the role of CTLs in helminth infection is limited. Atleast in mice, there is evidence to show that CTL population is dispensable for anti-helminth immunity . In clinical studies, LF infection was shown to upregulate HLA-A thereby activating CTLs . However, these activated CTLs showed poor proliferative response under
3.3 B cells in insulin resistance and immunomodulation
B cells form a major component of adaptive immunity and perform two vital functions namely: 1. Antigen presentation to T cells which links innate and adaptive arms of the immune response and 2. Production of antibodies which perform the effector functions. In obese mice, B cells were found to migrate into the adipose tissue shortly after the initiation of a high-fat diet . The initial signal for B cell activation is provided by the stressed adipocytes by releasing the self-antigens . The activated B cells then induce the activation of pro-inflammatory macrophages and T cells and the production of auto-antibodies . Correspondingly, increased IgG production (predominantly of IgG2c subtype) and increased IgG+ B cells were seen in the VAT of obese mice [102, 103]. B cell null mice showed reduced immune cell activation and IR in VAT and transfer of IgG antibodies from obese wild type mice to B cell null obese mice worsened glucose tolerance . The IgG antibodies, apart from promoting B cell-mediated adipose inflammation, can also bind to Fc receptors present on macrophages, NK cells, neutrophils and eosinophils, and can bring about cellular activation augmenting inflammation [102, 104]. However, recently ZnT8 specific naturally occurring autoantibodies were found to be significantly reduced in type-2 diabetes, indicating a beneficial effect for these antibodies in reducing IR .
The function of B cells in helminth infection is largely restricted to the protective Th2 response . IL-4 mediated activation, class switching and affinity maturation of B cells are responsible for the elevated levels of IgE antibodies in infected individuals . In streptozotocin-induced diabetic mice, treatment with
4. Conclusion and future directions
A decrease in helminth infections (like lymphatic filariasis) could potentially account for the increased prevalence of metabolic diseases in the western world. The same immunomodulatory effect can have an impact on type-2 diabetes, as was seen in tropical countries. Recently, several helminth antigens were shown to confer significant protection against obesity, insulin resistance and diabetes, in animal models. The implications of helminth induced immunomodulation are thus twofold: Mass drug administration in populations which are highly susceptible to type-2 diabetes has to be carried out with care; Secondly, more research is needed in identifying and characterizing novel helminth antigens with a strong immunomodulatory effect which can later be developed into diabetes vaccines.
Hotamisligil GS. Inflammation and metabolic disorders. Nature. 2006; 444: 860-867.
Aravindhan V, Madhumitha H. Metainflammation in Diabetic Coronary Artery Disease: Emerging Role of Innate and Adaptive Immune Responses. J Diabetes Res. 2016; 2016:6264149.
Aravindhan V, Anand G. Cell Type-Specific Immunomodulation Induced by Helminthes: Effect on Metainflammation, Insulin Resistance and Type-2 Diabetes. Am J Trop Med Hyg. 2017;97:1650-1661.
Strachan DP. Hay fever, hygiene, and household size. BMJ. 1989;299:1259-1260.
Alexandre-Silva GM, Brito-Souza PA, Oliveira ACS, Cerni FA, Zottich U, Pucca MB. The hygiene hypothesis at a glance: Early exposures, immune mechanism and novel therapies. Acta Trop. 2018;188:16-26.
Gao S, Wang S, Song Y. Novel immunomodulatory drugs and neo-substrates. Biomark Res. 2020;8:2.
Caraballo L. The tropics, helminth infections and hygiene hypotheses. Expert Rev Clin Immunol. 2018;14:99-102.
Aravindhan V, Mohan V, Surendar J, Rao MM, Ranjani H, Kumaraswami V, et al. Decreased prevalence of lymphatic filariasis among subjects with type-1 diabetes. Am J Trop Med Hyg. 2010;83:1336-1339.
Aravindhan V, Mohan V, Surendar J, Muralidhara Rao M, Pavankumar N, Deepa M, et al. Decreased prevalence of lymphatic filariasis among diabetic subjects associated with a diminished pro-inflammatory cytokine response (CURES 83). PLoS Negl Trop Dis. 2010;4:e707.
Aravindhan V, Mohan V, Surendar J, Rao MM, Anuradha R, Deepa M, et al. Effect of filarial infection on serum inflammatory and atherogenic biomarkers in coronary artery disease (CURES-121). Am J Trop Med Hyg. 2012;86:828-833.
de Ruiter K, Tahapary DL, Sartono E, Soewondo P, Supali T, Smit JWA, et al. Helminths, hygiene hypothesis and type 2 diabetes. Parasite Immunol. 2017;39.
Shanker A, Thounaojam MC, Mishra MK, Dikov MM. Innate-Adaptive Immune Crosstalk 2016. J Immunol Res. 2017;2017:3503207.
Tsuji T. Subcutaneous fat necrosis of the newborn: Light and electron microscopic studies. Br J Dermatol. 1976;95:407-416.
Oishi Y, Manabe I. Macrophages in inflammation, repair and regeneration. Int Immunol. 2018;30:511-528.
Russo L, Lumeng CN. Properties and functions of adipose tissue macrophages in obesity. Immunology. 2018;155:407-417.
Buechler C, Schaffler A. Does global gene expression analysis in type 2 diabetes provide an opportunity to identify highly promising drug targets? Endocr Metab Immune Disord Drug Targets. 2007;7:250-258.
Kumar V. Macrophages: The Potent Immunoregulatory Innate Immune Cells. In: Bhat KH, editor. Macrophage Activation Biology and Disease: IntechOpen; 2020.
Madhumitha H, Mohan V, Babu S, Aravindhan V. TLR-induced secretion of novel cytokine IL-27 is defective in newly diagnosed type-2 diabetic subjects. Cytokine. 2018;104:65-71.
Madhumitha H, Mohan V, Kumar NP, Pradeepa R, Babu S, Aravindhan V. Impaired toll-like receptor signalling in peripheral B cells from newly diagnosed type-2 diabetic subjects. Cytokine. 2015;76:253-259.
Faz-Lopez B, Morales-Montor J, Terrazas LI. Role of Macrophages in the Repair Process during the Tissue Migrating and Resident Helminth Infections. Biomed Res Int. 2016;2016:8634603.
Smith H, Forman R, Mair I, Else KJ. Interactions of helminths with macrophages: therapeutic potential for inflammatory intestinal disease. Expert Rev Gastroenterol Hepatol. 2018;12:997-1006.
Berbudi A, Surendar J, Ajendra J, Gondorf F, Schmidt D, Neumann AL, et al. Filarial Infection or Antigen Administration Improves Glucose Tolerance in Diet-Induced Obese Mice. J Innate Immun. 2016;8:601-616.
Yang Z, Grinchuk V, Smith A, Qin B, Bohl JA, Sun R, et al. Parasitic nematode-induced modulation of body weight and associated metabolic dysfunction in mouse models of obesity. Infect Immun. 2013;81:1905-1914.
Amdare N, Khatri V, Yadav RS, Tarnekar A, Goswami K, Reddy MV. Brugia malayi soluble and excretory-secretory proteins attenuate development of streptozotocin-induced type 1 diabetes in mice. Parasite Immunol. 2015;37:624-634.
Amdare NP, Khatri VK, Yadav RSP, Tarnekar A, Goswami K, Reddy MVR. Therapeutic potential of the immunomodulatory proteins Wuchereria bancrofti L2 and Brugia malayi abundant larval transcript 2 against streptozotocin-induced type 1 diabetes in mice. J Helminthol. 2017;91:539-548.
Imai S, Tezuka H, Fujita K. A factor of inducing IgE from a filarial parasite prevents insulin-dependent diabetes mellitus in nonobese diabetic mice. Biochem Biophys Res Commun. 2001;286:1051-8.
Morimoto M, Azuma N, Kadowaki H, Abe T, Suto Y. Regulation of type 2 diabetes by helminth-induced Th2 immune response. J Vet Med Sci. 2017;78:1855-1864.
Hussaarts L, Garcia-Tardon N, van Beek L, Heemskerk MM, Haeberlein S, van der Zon GC, et al. Chronic helminth infection and helminth-derived egg antigens promote adipose tissue M2 macrophages and improve insulin sensitivity in obese mice. FASEB J. 2015;29:3027-3039.
Sundara Rajan S, Longhi MP. Dendritic cells and adipose tissue. Immunology. 2016;149:353-361.
Stefanovic-Racic M, Yang X, Turner MS, Mantell BS, Stolz DB, Sumpter TL, et al. Dendritic cells promote macrophage infiltration and comprise a substantial proportion of obesity-associated increases in CD11c+ cells in adipose tissue and liver. Diabetes. 2012;61:2330-2339.
Surendar J, Mohan V, Pavankumar N, Babu S, Aravindhan V. Increased levels of serum granulocyte-macrophage colony-stimulating factor is associated with activated peripheral dendritic cells in type 2 diabetes subjects (CURES-99). Diabetes Technol Ther. 2012;14:344-349.
Motran CC, Ambrosio LF, Volpini X, Celias DP, Cervi L. Dendritic cells and parasites: from recognition and activation to immune response instruction. Semin Immunopathol. 2017;39:199-213.
Schuijs MJ, Hammad H, Lambrecht BN. Professional and ‘Amateur’ Antigen-Presenting Cells In Type 2 Immunity. Trends Immunol. 2019;40:22-34.
Kane CM, Jung E, Pearce EJ. Schistosoma mansoni egg antigen-mediated modulation of Toll-like receptor (TLR)-induced activation occurs independently of TLR2, TLR4, and MyD88. Infect Immun. 2008;76:5754-5759.
Goodridge HS, Marshall FA, Wilson EH, Houston KM, Liew FY, Harnett MM, et al. In vivo exposure of murine dendritic cell and macrophage bone marrow progenitors to the phosphorylcholine-containing filarial nematode glycoprotein ES-62 polarizes their differentiation to an anti-inflammatory phenotype. Immunology. 2004;113:491-498.
Sharma A, Sharma P, Vishwakarma AL, Srivastava M. Functional Impairment of Murine Dendritic Cell Subsets following Infection with Infective Larval Stage 3 of Brugia malayi. Infect Immun. 2017;85.
Hussaarts L, Yazdanbakhsh M, Guigas B. Priming dendritic cells for th2 polarization: lessons learned from helminths and implications for metabolic disorders. Front Immunol. 2014;5:499.
Mantovani A, Cassatella MA, Costantini C, Jaillon S. Neutrophils in the activation and regulation of innate and adaptive immunity. Nat Rev Immunol. 2011;11:519-531.
Kumar V, Sharma A. Neutrophils: Cinderella of innate immune system. Int Immunopharmacol. 2010;10:1325-1334.
Talukdar S, Oh DY, Bandyopadhyay G, Li D, Xu J, McNelis J, et al. Neutrophils mediate insulin resistance in mice fed a high-fat diet through secreted elastase. Nat Med. 2012;18:1407-1412.
Allen JE, Sutherland TE, Ruckerl D. IL-17 and neutrophils: unexpected players in the type 2 immune response. Curr Opin Immunol. 2015;34:99-106.
Deniset JF, Kubes P. Neutrophil heterogeneity: Bona fide subsets or polarization states? J Leukoc Biol. 2018;103:829-838.
Kannan Y, Entwistle LJ, Pelly VS, Perez-Lloret J, Walker AW, Ley SC, et al. TPL-2 restricts Ccl24-dependent immunity to Heligmosomoides polygyrus. PLoS Pathog. 2017;13:e1006536.
O’Connell AE, Hess JA, Santiago GA, Nolan TJ, Lok JB, Lee JJ, et al. Major basic protein from eosinophils and myeloperoxidase from neutrophils are required for protective immunity to Strongyloides stercoralis in mice. Infect Immun. 2011;79:2770-2778.
Anbu KA, Joshi P. Identification of a 55 kDa Haemonchus contortus excretory/secretory glycoprotein as a neutrophil inhibitory factor. Parasite Immunol. 2008;30:23-30.
Rothenberg ME, Hogan SP. The eosinophil. Annu Rev Immunol. 2006;24:147-174.
Wu D, Molofsky AB, Liang HE, Ricardo-Gonzalez RR, Jouihan HA, Bando JK, et al. Eosinophils sustain adipose alternatively activated macrophages associated with glucose homeostasis. Science. 2011;332:243-247.
Rozenberg P, Reichman H, Zab-Bar I, Itan M, Pasmanik-Chor M, Bouffi C, et al. CD300f:IL-5 cross-talk inhibits adipose tissue eosinophil homing and subsequent IL-4 production. Sci Rep. 2017;7:5922.
Strandmark J, Rausch S, Hartmann S. Eosinophils in Homeostasis and Their Contrasting Roles during Inflammation and Helminth Infections. Crit Rev Immunol. 2016;36:193-238.
Gebreselassie NG, Moorhead AR, Fabre V, Gagliardo LF, Lee NA, Lee JJ, et al. Eosinophils preserve parasitic nematode larvae by regulating local immunity. J Immunol. 2012;188:417-425.
Guigas B, Molofsky AB. A worm of one’s own: how helminths modulate host adipose tissue function and metabolism. Trends Parasitol. 2015;31:435-441.
Varricchi G, Raap U, Rivellese F, Marone G, Gibbs BF. Human mast cells and basophils-How are they similar how are they different? Immunol Rev. 2018;282:8-34.
Kumar V, Sharma A. Mast cells: emerging sentinel innate immune cells with diverse role in immunity. Mol Immunol. 2010;48:14-25.
Altintas MM, Azad A, Nayer B, Contreras G, Zaias J, Faul C, et al. Mast cells, macrophages, and crown-like structures distinguish subcutaneous from visceral fat in mice. J Lipid Res. 2011;52:480-488.
Liu J, Divoux A, Sun J, Zhang J, Clement K, Glickman JN, et al. Genetic deficiency and pharmacological stabilization of mast cells reduce diet-induced obesity and diabetes in mice. Nat Med. 2009;15:940-945.
Wang J, Shi GP. Mast cell stabilization: novel medication for obesity and diabetes. Diabetes Metab Res Rev. 2011;27:919-924.
Mitre E, Nutman TB. Basophils, basophilia and helminth infections. Chem Immunol Allergy. 2006;90:141-156.
Hartmann W, Linnemann LC, Reitz M, Specht S, Voehringer D, Breloer M. Basophils Are Dispensable for the Control of a Filarial Infection. Immunohorizons. 2018;2:296-304.
Mitre E, Taylor RT, Kubofcik J, Nutman TB. Parasite antigen-driven basophils are a major source of IL-4 in human filarial infections. J Immunol. 2004;172:2439-2445.
Saini SS, Klion AD, Holland SM, Hamilton RG, Bochner BS, Macglashan DW, Jr. The relationship between serum IgE and surface levels of FcepsilonR on human leukocytes in various diseases: correlation of expression with FcepsilonRI on basophils but not on monocytes or eosinophils. J Allergy Clin Immunol. 2000;106:514-520.
Makepeace BL, Martin C, Turner JD, Specht S. Granulocytes in helminth infection -- who is calling the shots? Curr Med Chem. 2012;19:1567-1586.
Spencer LA, Porte P, Zetoff C, Rajan TV. Mice genetically deficient in immunoglobulin E are more permissive hosts than wild-type mice to a primary, but not secondary, infection with the filarial nematode Brugia malayi. Infect Immun. 2003;71:2462-2467.
Min B. Basophils induce Th2 immunity: is this final answer? Virulence. 2010;1:399-401.
Abel AM, Yang C, Thakar MS, Malarkannan S. Natural Killer Cells: Development, Maturation, and Clinical Utilization. Front Immunol. 2018;9:1869.
Godfrey DI, Hammond KJ, Poulton LD, Smyth MJ, Baxter AG. NKT cells: facts, functions and fallacies. Immunol Today. 2000;21:573-583.
Bonamichi B, Lee J. Unusual Suspects in the Development of Obesity-Induced Inflammation and Insulin Resistance: NK cells, iNKT cells, and ILCs. Diabetes Metab J. 2017;41:229-250.
O’Rourke RW, Metcalf MD, White AE, Madala A, Winters BR, Maizlin, II, et al. Depot-specific differences in inflammatory mediators and a role for NK cells and IFN-gamma in inflammation in human adipose tissue. Int J Obes (Lond). 2009;33:978-990.
Lynch L, Nowak M, Varghese B, Clark J, Hogan AE, Toxavidis V, et al. Adipose tissue invariant NKT cells protect against diet-induced obesity and metabolic disorder through regulatory cytokine production. Immunity. 2012;37:574-587.
Babu S, Blauvelt CP, Nutman TB. Filarial parasites induce NK cell activation, type 1 and type 2 cytokine secretion, and subsequent apoptotic cell death. J Immunol. 2007;179:2445-2456.
Korten S, Volkmann L, Saeftel M, Fischer K, Taniguchi M, Fleischer B, et al. Expansion of NK cells with reduction of their inhibitory Ly-49A, Ly-49C, and Ly-49G2 receptor-expressing subsets in a murine helminth infection: contribution to parasite control. J Immunol. 2002;168:5199-5206.
Faveeuw C, Mallevaey T, Trottein F. Role of natural killer T lymphocytes during helminthic infection. Parasite. 2008;15:384-388.
Gabrilovich DI, Nagaraj S. Myeloid-derived suppressor cells as regulators of the immune system. Nat Rev Immunol. 2009;9:162-174.
Wang T, Wen Y, Fan X. Myeloid-derived suppressor cells suppress CD4+ T cell activity and prevent the development of type 2 diabetes. Acta Biochim Biophys Sin (Shanghai). 2018;50:362-9.
Xia S, Sha H, Yang L, Ji Y, Ostrand-Rosenberg S, Qi L. Gr-1+ CD11b+ myeloid-derived suppressor cells suppress inflammation and promote insulin sensitivity in obesity. J Biol Chem. 2011;286:23591-23599.
Brys L, Beschin A, Raes G, Ghassabeh GH, Noel W, Brandt J, et al. Reactive oxygen species and 12/15-lipoxygenase contribute to the antiproliferative capacity of alternatively activated myeloid cells elicited during helminth infection. J Immunol. 2005;174:6095-6104.
Yang Q , Qiu H, Xie H, Qi Y, Cha H, Qu J, et al. A Schistosoma japonicum Infection Promotes the Expansion of Myeloid-Derived Suppressor Cells by Activating the JAK/STAT3 Pathway. J Immunol. 2017;198:4716-4727.
Vivier E, Artis D, Colonna M, Diefenbach A, Di Santo JP, Eberl G, et al. Innate Lymphoid Cells: 10 Years On. Cell. 2018;174:1054-1066.
Kumar V. Innate lymphoid cells: new paradigm in immunology of inflammation. Immunol Lett. 2014;157:23-37.
Kumar V. Innate Lymphoid Cells: Immunoregulatory Cells of Mucosal Inflammation. European Journal of Inflammation. 2014;12:11-20.
O’Sullivan TE, Rapp M, Fan X, Weizman OE, Bhardwaj P, Adams NM, et al. Adipose-Resident Group 1 Innate Lymphoid Cells Promote Obesity-Associated Insulin Resistance. Immunity. 2016;45:428-441.
Brestoff JR, Kim BS, Saenz SA, Stine RR, Monticelli LA, Sonnenberg GF, et al. Group 2 innate lymphoid cells promote beiging of white adipose tissue and limit obesity. Nature. 2015;519:242-246.
Loser S, Smith KA, Maizels RM. Innate Lymphoid Cells in Helminth Infections-Obligatory or Accessory? Front Immunol. 2019;10:620.
Hams E, Bermingham R, Wurlod FA, Hogan AE, O’Shea D, Preston RJ, et al. The helminth T2 RNase omega1 promotes metabolic homeostasis in an IL-33- and group 2 innate lymphoid cell-dependent mechanism. FASEB J. 2016;30:824-835.
Kumar BV, Connors TJ, Farber DL. Human T Cell Development, Localization, and Function throughout Life. Immunity. 2018;48:202-213.
Wang Q , Wu H. T Cells in Adipose Tissue: Critical Players in Immunometabolism. Front Immunol. 2018;9:2509.
Winer S, Chan Y, Paltser G, Truong D, Tsui H, Bahrami J, et al. Normalization of obesity-associated insulin resistance through immunotherapy. Nat Med. 2009;15:921-929.
Feuerer M, Herrero L, Cipolletta D, Naaz A, Wong J, Nayer A, et al. Lean, but not obese, fat is enriched for a unique population of regulatory T cells that affect metabolic parameters. Nat Med. 2009;15:930-939.
O’Rourke RW, White AE, Metcalf MD, Winters BR, Diggs BS, Zhu X, et al. Systemic inflammation and insulin sensitivity in obese IFN-gamma knockout mice. Metabolism. 2012;61:1152-1161.
Stanya KJ, Jacobi D, Liu S, Bhargava P, Dai L, Gangl MR, et al. Direct control of hepatic glucose production by interleukin-13 in mice. J Clin Invest. 2013;123:261-271.
Surendar J, Mohan V, Rao MM, Babu S, Aravindhan V. Increased levels of both Th1 and Th2 cytokines in subjects with metabolic syndrome (CURES-103). Diabetes Technol Ther. 2011;13:477-482.
Tao L, Liu H, Gong Y. Role and mechanism of the Th17/Treg cell balance in the development and progression of insulin resistance. Mol Cell Biochem. 2019;459:183-188.
Surendar J, Aravindhan V, Rao MM, Ganesan A, Mohan V. Decreased serum interleukin-17 and increased transforming growth factor-beta levels in subjects with metabolic syndrome (Chennai Urban Rural Epidemiology Study-95). Metabolism. 2011;60:586-590.
Cipolletta D, Feuerer M, Li A, Kamei N, Lee J, Shoelson SE, et al. PPAR-gamma is a major driver of the accumulation and phenotype of adipose tissue Treg cells. Nature. 2012;486:549-553.
Anand G, Vasanthakumar R, Mohan V, Babu S, Aravindhan V. Increased IL-12 and decreased IL-33 serum levels are associated with increased Th1 and suppressed Th2 cytokine profile in patients with diabetic nephropathy (CURES-134). Int J Clin Exp Pathol. 2014;7:8008-8015.
Madhumitha H, Mohan V, Deepa M, Babu S, Aravindhan V. Increased Th1 and suppressed Th2 serum cytokine levels in subjects with diabetic coronary artery disease. Cardiovasc Diabetol. 2014;13:1.
Vasanthakumar R, Mohan V, Anand G, Deepa M, Babu S, Aravindhan V. Serum IL-9, IL-17, and TGF-beta levels in subjects with diabetic kidney disease (CURES-134). Cytokine. 2015;72:109-112.
Babu S, Nutman TB. Immunology of lymphatic filariasis. Parasite Immunol. 2014;36:338-346.
Su CW, Chen CY, Li Y, Long SR, Massey W, Kumar DV, et al. Helminth infection protects against high fat diet-induced obesity via induction of alternatively activated macrophages. Sci Rep. 2018;8:4607.
Nishimura S, Manabe I, Nagasaki M, Eto K, Yamashita H, Ohsugi M, et al. CD8+ effector T cells contribute to macrophage recruitment and adipose tissue inflammation in obesity. Nat Med. 2009;15:914-920.
Rajan TV, Nelson FK, Shultz LD, Koller BH, Greiner DL. CD8+ T lymphocytes are not required for murine resistance to human filarial parasites. J Parasitol. 1992;78:744-746.
Kalinkovich A, Weisman Z, Greenberg Z, Nahmias J, Eitan S, Stein M, et al. Decreased CD4 and increased CD8 counts with T cell activation is associated with chronic helminth infection. Clin Exp Immunol. 1998;114:414-421.
Winer DA, Winer S, Shen L, Wadia PP, Yantha J, Paltser G, et al. B cells promote insulin resistance through modulation of T cells and production of pathogenic IgG antibodies. Nat Med. 2011;17:610-617.
Mallat Z. The B-side story in insulin resistance. Nat Med.17:539-40.
Nokoff NJ, Rewers M, Cree Green M. The interplay of autoimmunity and insulin resistance in type 1 diabetes. Discov Med. 2012;13:115-122.
Hussaarts L, van der Vlugt LE, Yazdanbakhsh M, Smits HH. Regulatory B-cell induction by helminths: implications for allergic disease. J Allergy Clin Immunol. 2011;128:733-739.