Open access peer-reviewed chapter

The Immunomodulatory Role of Probiotics

Written By

Faisal Siddique, Kashif Akram, Etab Saleh Alghamdi, Qandeel Arshad and Ayesha Siddique

Submitted: May 19th, 2021 Reviewed: June 11th, 2021 Published: April 6th, 2022

DOI: 10.5772/intechopen.98839

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Probiotics are particularly beneficial living microorganisms that help improve human health. Although probiotics have long been used as nutritional supplements in various cultures around the world, new research has investigated their antimicrobial and immune boosting effects in individuals. Lactobacillus and Bifidobacterium are popular probiotics used worldwide that benefit human health by acting as antibacterial, antiviral, and antifungal agents, reducing pathogen binding to the host receptor and thus capturing pathogenic microorganisms. Probiotics have been shown to be beneficial in a variety of bacterial and viral diseases worldwide. The regulation of the host’s immune response is one of the most important mechanisms of probiotic action. Immunomodulatory effects of probiotic-derived compounds have been characterized using genomic and proteomic analysis. These compounds have the ability to regulate and initiate mucosal immunity against various diseases. Probiotics produce many bactericidal compounds, which inhibit the growth of pathogenic microorganisms and their toxins, promoting the sustainability and structural integrity of enterocytes. This chapter focused on recent scientific research findings that help us better understand how probiotics regulate the host immune response and how they can be used to prevent and treat disease and there beneficial role to improve the health status of individuals.


  • Immunomodulatory
  • Antibacterial
  • Antiviral
  • Probiotics
  • Lactobacillus

1. Introduction

The human body is prone to many virulent microbes and their oxidative metabolic substances. The human body is shielded from potentially pathogenic microbes by the immune system [1]. The gastrointestinal tract, which is approximately 7.5 meters long, is the largest area of the immune system. Furthermore, trillions of bacteria reside in the gut, particularly in the colon, which served as the main reservoir for these mutualistic species. Most of the time, it is said that the number of human cells in the body is ten times less than that of bacterial cells, while this proportion has been revamped to about 1:1 [2]. Normal vaginal and fecal microorganisms were injected at birth to study the host microbe’s relationship with the newborn. This inoculum contains aerobic, anaerobic, gram-positive, and gram-negative bacteria belonging to dominant species such as Sneathia spp., Lactobacillus spp., and Prevotella spp. [3]. It has been studied that how gestational stage, environment, type of delivery, attitude, and breastfeeding habits influenced the proliferation and stability of the infant’s microbiome [4].

The host-microbe relationship is critical for the growth of the gastrointestinal immunity within the first weeks after giving birth. The proliferation and growth of gut microorganisms continues until about the age of two years, at which point the intestinal immune system is said to be mature [5]. The intestinal environment of gut microorganisms is generally stable, particularly at the species and genus levels. Besides that, irrational antibiotic use, pathogenic parasites, malnutrition, or cold and hot stress all have an impact on the structural composition of gut microbiota [6].

Antimicrobial drugs, as well as human-targeted medicines, have been attributed to changes in gut microbial composition. More than a thousand antimicrobial drugs have been evaluated against forty different intestinal bacteria around the world. They discover 24 drugs that inhibit the growth of one or even more bacterial strains in vitro [7]. The defensive mechanism is triggered by innate immunity when an individual’s body is exposed to a foreign particle or sustains tissue damage. Innate immunity protects cells physiology by signaling adaptive immune responses to persistent threats and stimulating inflammatory response. Inconsistent innate and adaptive responses, on the other hand, result in highly inflammatory reactions, tissue damage, and disease. The host mucosal immune response induced by gut microbiota is important for maintaining intestinal homeostasis and developing a systemic defense response. Manipulation of the intestinal microbiota can thus be a viable alternative route to improving health and to prevent and/or cure illness [8].

Probiotics were described as ‘live microorganisms that impart benefits to the host health when taken in sufficient quantities as component of food”. Saccharomyces, Lactobacillus, and Bifidobacterium are three important probiotic Genus that have been extensively researched and used in animal and human feed [9]. Recent research indicates that probiotics have a number of beneficial effects on the host’s gastrointestinal tract protection mechanism. They produce bactericidal substances by which they counteract pathogenic microorganisms’ consequences and bind to the intestinal epithelium by interacting with pathogenic microorganisms and their toxins. Probiotics facilitate the longevity of epithelial cells, improve the immune barrier, and improve the immune response to intestinal epithelium, all of which lead to gastric mucosal homeostasis [10]. Most notably, immune system regulation is among the most potential factors behind probiotics’ beneficial health effects. Probiotics strengthen innate and adaptive immunity and suppress bacterial infection through toll-like receptor-regulated signal transduction pathways. Probiotic bacteria have been seen to enhance intrinsic host immune mechanisms. The use of probiotic microbes has significant effects on people’s immune systems, such as stabilizing the non-immunological or innate immune response triggered by gut microbes, improving adaptive intestinal immune response, and regulating non-specific inflammatory and hypersensitivity reactions [11].


2. Historical background of probiotics

The concept of probiotics therapy emerged after the discovery of gut microbiome that is an inherent part of the intestinal epithelial cells. A probiotic is represented as a live microorganism’s dietary supplement that benefits the individual by boosting the intestinal microbiome in the gastrointestinal tract. The probiotic definition is incomplete for the aim of human health and nutrition. In response, the European Commission and the International Institute of Life Sciences collaborated to reframe the concept of probiotics as a live microbial food item which is beneficial to human health [12].

In 1953, German researcher Werner Kollath coined the term probiotic, which is comes from the Latin terms pro, which means for, and biotic, which means “bios” or “life.” Probiotics were defined by Lilly and Stillwell in 1965 as substances produced naturally by one microorganism that promotes the growth of another. In 1992, Fuller described probiotics as “live microorganisms added as a supplement in feed that benefits the host by improving its intestinal microbial balance” Probiotics have a modern history dating back to the early 1900s, when future Nobel laureate Elie Metchnikoff, a Russian scientist working at the Pasteur Institute in Paris, performed groundbreaking research [13].

Louis Pasteur established the microbes required for the fermentation process, while Metchnikoff first sought to determine the potential impact of the microbiota on public health. He attributed Bulgarian village peoples’ long life spans to their regular consumption of yoghurt, which are fermented dairy products. He related this to Stamen Grigorov, a physician who found the Bulgarian bacillus, and further proposed that lactobacilli could mitigate the decaying impact of digestive fermentation, that led to illness and aging. Furthermore, Socrates said over two thousand years ago that “death lies in the guts” and that “poor absorption is the root of all evil.” Metchnikoff also reported that toxins generated by microbial decomposition in the gastrointestinal tract and then discharged into to the bloodstream trigger aging [14]. Such microbes were originally referred to as decomposing microbes, but they are now known as proteolytic clostridia. Metchnikoff also noted that “the gastrointestinal microbiota’ reliance on food allows us to take steps to change the microbiome in our gastrointestinal tract and exchange pathogenic microorganisms with good bacteria.” Metchnikoff scientific theory of probiotics was the foundation for the first dairy industry in France [15].

Modern techniques have selected probiotics strains that manufacture fortified milk with strong nutritional and organoleptic features more than anyone else. Yoghurt was the first functional fermented food based to historical evidence [16]. However, since probiotics are usually associated to the consumption of fermented foods, they have a long and distinguished history. In ancient Indian Vedic literature, milk and milk products are associated to a reliable and comfortable life. According to legend, the first kefir grain was distributed by Prophet Muhammad (SAW) to the descendants of Caucasian mountaineers as a reward. Kefir is a fermented milk drink that contains a lot of lactic acid bacteria and probiotics. Cheese and yoghurt have been used by Hippocrates, Marco Polo, Galeno, and Chinese people throughout history [17].


3. Probiotics stimulate innate immune system

The most distinguished cells of natural immunity in probiotic research are the dendritic and epithelial cells. These are the first cells to interact with the gut microbiota and its toxic metabolites. Gut associated lymphoid tissue (GALT) and intestinal mucosa is the reservoir of intestinal dendritic cells. Dendritic cells are also known as detector cells because they have unique receptors that attach to specific sites on pathogen surfaces. Dendritic cells also act as a catalyst for various forms of signaling pathways that modify phenotypes and secreted cytokines such as Toll-like receptors and c-type lectin receptors [18].

Bifidobacterium infantis 35624 is a probiotic strain that can regulate dendritic cells activity, leading to a rise in cDC1 (CD103+ DC) in the basal lamina. It has many advantages for human health because it decreases the incidence of Dextran sulphate sodium-induced colitis, which is caused by a retinoid acid-dependent process [19]. Furthermore, oral administration of B. infantis 14.518 to Albino BALB/C mice stimulates the growth, development, and maturation of dendritic cells in GALT, which is responsible for the regulation of T cells and the inhibition of Th2-biased responses through a process known as differentiation [20]. Additionally, other B. longum, B. infantis, L. rhamnosus, and L. casei enhance CCR7, CD40, and CD80 production in both juvenile and old Dendritic cells donors, whereas only old donors can boost IFN-γ and TGF- expression. The oral administration of B. longum bv. infantis CCUG increased IL-10 output [21].

The use of probiotic strain L. rhamnosus JB-1 has many advantages to regulate the dendritic cells by production of haemoxygense, stimulation of DC-SIGN and TLR-2 pattern recognition receptors (PRRs). L. rhamnosus JB-1 helps reduce inflammation via inhibiting the expression of co-stimulatory molecules, production and maturation of cytokines and TH1/TH17 through stimulations of the human monocyte derived dendritic cells. The immunomodulatory activity of L. rhamnosus JB-1, which expresses Foxp3 and induces IL-10 development, has been documented. Probiotic bacterial strain cell wall components also regulate the immunomodulation of DCs. When capsular polysaccharide binds with TLR-2 receptors on dendritic cells, it stimulates the development of IL-10 from T helper cells, which reduces the inflammatory response caused by colitis [22]. Similarly, exo-polysaccharides derived from Bacillus subtilis are useful in the treatment of intestinal infections because they protect against Citrobacter rodentiumin toxicity. Probiotics, on the other hand, control the microbial populations in the intestine after modifying dendritic cells activation [23].

The absorptive role of intestinal epithelium is well described. Epithelial cells produce a mucosal barrier to safeguard the individual from harmful microbes and toxicants. The intestinal mucosa barrier has a powerful connection with the intrinsic immune system of the Peyer’s patches and lamina propria [24]. Probiotics are well-known for preserving the integrity of the intestinal barrier through a variety of mechanisms, including starvation of infectious agents as they compete for nutrients, detachment of bacteria from intestinal epithelium, which prevents pathogen invasion, immune response regulation, and aiding in regulatory T cell responses. Most of these are probiotics’ positive effects on the host’s internal health [25]. The use of B. infantis prevents Salmonella infection by reducing the induction of Peyer’s patch macrophage inflammatory protein-1 (MIP)-1 and MIP-1 through a Treg-dependent pathway [26]. Human-defensin-2 is a probiotic-produced antimicrobial peptide that strengthens the mucosal barrier against pathogenic microbes. Defensins are wide ranging anti-microbial peptides released by macrophages, epithelial cells, neutrophils and, Paneth cells as part of a natural immune reaction [27]. Shirota strain (L. casei) increases defensin mRNA transcription in Caco-2 colonic intestinal cells by increasing hBD-2 [28].

Multiple probiotic strains of the genus Bifidobacterium, such as B. infantis, B. adolescentis, B. bifidum, and B. longum, could be modulate the apoptosis process in intestinal epithelial cells. They can also enhance mucin secretion, which serves as the first line of protection against infectious agents in the intestine [29]. L. rhamnosus GG3 induces mucin production in intestinal epithelial cells by activating the Muc2 and p40 genes expression. When an antigen attaches to enterocytes, pro-inflammatory neurotransmitters, chemokine’s, and some tumor necrosis factor are secreted, triggering an efficient immune response [30]. L. casei and L. rhamnosus reduce the production of proinflammatory cytokines in enterocytes after infection with Clostridium difficile. B. polyfermenticus, Bifidobacterium lactus, B. animalis ssp. lactis Lactobacillus casei, L. paracasei ssp. paracasei, and L. plantarum stimulate the production of natural killer cells after infection [31].


4. Probiotics stimulate humoral immune system

Probiotics are used to sensitize the host’s immune system to potentially dangerous pathogens. Oral administration of B. bifidum increased humoral immune response to egg albumin, whereas B. breve increased IgA exposure to cholera toxin [32]. Oral administration of L. rhamnosus triggered antibody IgA secreted B-cells in children with rotavirus infection in control studies [33]. Lactobacilli were given orally to suckling rats that had been sensitized with cow milk, and the number of cells secreting antibodies β-lactoglobulin increased. Human babies develop atopic dermatitis after consuming cow milk. Probiotic therapy, on the other hand, has been scientifically proven to minimize atopic dermatitis infection in humans. Food antigens are processed in the intestine with the aid of the gut microbiota. Low-molecular-weight peptides produced by bacteria collected from of the gastric microbiota can stimulate the immune reaction [34].

Probiotic derived proteases have been shown to digest cow milk casein and produce peptides that inhibit inflammatory cytokines in healthy people. A study was conducted to see whether caseins digested by probiotic bacteria producing proteases might induce the production of cytokine and anti-CD3 immunoglobulin mononuclear cells in atopic dermatitis in infants with cow milk allergies. Casein from cow’s milk stimulates the synthesis of IL-4, which causes hypersensitivity [35]. Oral administration of L. rhamnosus GG, on the other hand, breaks down casein and inhibits IL-4 synthesis. These results indicate that probiotics in diet change the composition of potentially toxic pathogens, thus altering their immunogenicity function [36].

The ability of probiotics to increase the number of T-regulated lymphocytic cells contributes for their anti-inflammatory and anti-colitis properties. B. longum has helped in the treatment of colorectal colitis in mice by upregulating T-regulated lymphocytic cells. As a result, IL-10 and IL-12 levels in the blood have risen, while inflammatory cytokines including IL-23, IL-12, and IL-27 have decreased [37]. In healthy people, B. infantis induces Foxp3 T-cells to become activated, which decreases the levels of inflammatory cytokines in psoriasis patients [38].

Probiotics strain produced short chain fatty acids molecules such as propionate, isobutyrate, acetate, butyrate etc., which directly or indirectly regulate the homeostasis of T-cells. Butyrate activates Foxp3+ cells and Treg cell production outside of the hypothalamus. Propionate regulated the production of T-cell by inhibiting histone deacetylase. Probiotics e.g. L. acidophilu, B. breve, L. gasseri, B. longum, B. longum subsp. infantis prevented the development of Th17 inflammatory cells, which are responsible for the pathogenesis and progression of different inflammatory diseases such as irritable bowel syndrome [39]. Further to that, L. rhamnosus GG and B. breve inhibit IL-17 and IL-23, which are necessary for Th17 growth, stability, and stimulation. INFγ and TNF-α was produced by various Lactobacillus and Bifidobacterium species, which inhibited the expansion of Th17 inflammatory cells. B. longum (JCM) increased IL-27 development, which has been linked to a reduction in the amount of IL-17 stimulating Th-17 cells [40].

Probiotics have the ability to shift the immune response from Th2 to Th1. L. casei can stimulate IL-12 development, polarizing the Th1 response and mitigating Th2 linked illnesses. L. rhamnosus curtails Th2 as well as Th17 cells and improves clinical symptoms of seasonal allergies, atopic dermatitis and psoriatic arthritis. Probiotic fermented dairy milk modified the allergic process triggered by ovo-albumin in rats, polarizing a Th1 instead of a Th2 pattern reaction and leading throughout the production of IgG rather than IgE, with increased concentration of IFN-γ and IL- 10 accountable immunomodulation [41].

Probiotics have a direct effect on the cells of the lamina propria and payers patches, resulting in an increase in IgA production cells. IgA plays an important function in the prevention of mucosal pathogens. Toxins are neutralized by IgA, which prevents pathogens bacteria from binding to intestinal epithelial cells. L. gasseri (SBT2055) has been shown in mice to activate the TLR2 signal pathway, which triggers IgA generating cells in the mucosa and payers patches of the small intestine. While B lymphocytes are responsible for production of specific immunoglobulin and are the primary players in the adaptive immune response, they can also deprecating antibodies by manufacturing IL-10 through inflammatory and chronic diseases. The use of probiotics during combination with influenza vaccine increased an individual’s total number of IgG and memory B-cells [42].


5. Role of probiotics as antibacterial

The oral cavity is a highly complex structure containing over 700 different types of bacteria. When there is a disturbance in this environment, abnormalities such as periodontal disease may occur, resulting in a reduction of indigenous microbial populations to the advantage of infectious agents. The causative agents of oral cavity disease are S. mutans, A. viscosus, F. nucleatum and P. gingivalis. Microbial resistance tends to be a safe way to battle against the establishing of bacterial pathogens with in oral ecosystem, and this fight might well be enabled by probiotic strains [43].

Anti-bacterial substances formed by probiotic strains included defensin, acetaldehydes, hydrogen peroxide, bacteriocins, organic acids, ethanol, and peptides. Peptides and bacteriocins, in general, are essential in increasing the vascular permeability of target cells that contributes to activation of the membrane permeability and, eventually, cell damage [44].

Probiotics have antibacterial effect, which is an essential feature. Bacteriocin synthesis may be one way to accomplish this antibacterial activity. Bacteriocins are produced by the industrial probiotic strains L. casei YIT 9029 and L. johnsonii LA1. The antimicrobial compound’s existence can be deduced from its behavior, which includes a limited inhibiting range, lack of function if administered with proteinases, and relatively tiny molecular weights [45]. L. amylovorus (DCE 471), L. johnsonii (LA1), and L. casei (YIT 9029) all developed bacteriocins that prevented helicobacter pylori infection in humans. Regrettably, H. pylorus was not inhibited by a fourth bacteriocin induced by L. acidophilus (IBB 801). This suggests that certain bacteriocins formed by unique probiotic strains may help to inhibit this specific bacterium [46].

The most commonly used probiotic strains are from the Lactobacillus genus, which is recognized as safe. Some researchers have explained the function of probiotics in the buccal mucosa during the last few decades. Intake of lactic acid bacteria containing items has been shown to mitigate dental caries of mutant streptococci, but the studied species were ATCC strains rather than standard probiotic species such as L. rhamnosus GG. It has been demonstrated that probiotic strains with good antibacterial activity are needed to eliminate or stop harmful bacteria [47]. Lactobacilli have long been considered to be able to produce antimicrobial compounds. Lactobacilli may produce organic acid compounds as a result of carbohydrate fermentation, which can intervene with the function of neighboring microbes via depressing the pH of the environment. Some probiotic strains produce bacteriocins, which are well-known types of microbial animosity. L. gasseri was abundant in healthier people’s oral mucosa and developed bacteriocin against pathogenic microbes. L. reuteri appears to be able to produce reuterin, a powerful antibacterial substance derived from glycerol fermentation [48].


6. Role of probiotics as antiviral

A number of microorganisms have been found in the human respiratory tract as the primary source of the respiratory virus. We may reduce the occurrence of disease development in humans by limiting the penetration of respiratory tract viruses into the membranes of mucosal epithelial cells. The human body contains a diverse community of mutually advantageous commensal bacteria known as microbiota [49]. Probiotics are microorganisms that have potential health benefits when eaten in a specific amount. There are two basic types of probiotics: Lactobacillus and Bifidobacterium and Both have a positive impact on human health since it acts as an antiviral agent, lowering the binding ability of viruses to the host receptor and thereby capturing the virus. Probiotics administering protects individuals from various respiratory viral infections like Respiratory syncytial virus, SARS-CoV-2, Influenza A virus. This antiviral activity was investigated by the strain’s specificity as well as the host immune status [50].

L. casei shirota (LcS) is a lactobacillus probiotic strain isolated from the oral microbiota. It has been stated that when Lcs was presented to influenza (H1N1) infected mice, the viral titer declined. Furthermore, LcS stimulates the innate or nonspecific immune system by increasing the production of antiviral cytokines like IFN-α. Another study discovered immunomodulatory activity against Respiratory syncytial virus. LcS, on the other hand, has shown negligible findings into clinical trials, especially among older community, when compared to the control group [51]. Clinical trials were conducted on L. Casei (DN-114,001) demonstrated substantial antiviral activity in separate studies in infants, adults, and the elderly. It decreases the clinical signs and symptoms of respiratory tract infection in infants, adults, and the elderly [52].

L. fermentum is a bacteria present in both people and animals microbiota and is commonly used it as a probiotic in people. This probiotic was tested in clinical studies, specifically in children and young adults, as well as lab animals to examine the process of viral prevention toward respiratory infections. The efficacy of L. fermentum CJL-112 and L. fermentum-1 have been studied against Influenza virus (H1N1) infected with mice and the findings indicate a marked decline in viral count, with significant stimulation of IL-12 and Immunoglobulin (IgA) development, allowing for an improvement in mouse longevity. The combined effect of probiotic (L. fermentum CECT5716) and prebiotic (galacto-oligosaccharides) had assessed in healthy infants, and this research showed a significant decrease in the incidence of urinary and respiratory tract illness [53].

L. acidophilus is a well-known lactic acid bacteria strain that is used in medicinal treatments. Since L. acidophilus is commonly used to treat gastrointestinal issues, just few researchers have examined into its antiviral activity. L. acidophilus L-92, retrieved from a healthy Japanese citizen, demonstrated antiviral activity against influenza virus through IFN-α and natural killer cell modulation. The antiviral activity of L. brevis KB-290 against H1NI was examined, and virus levels were found to be depleted as a result of IgA and IFN-α stimulation [54]. Bifidobacteria aids in digestion, immunity, and the prevention of almost all gastrointestinal infections. These strains have been used in several clinical studies against viral respiratory diseases to determine the mechanism of antiviral effect [55].

B. longum (BB536) demonstrated anti-H1N1 activity in mice after parenteral route for two weeks prior to disease, owing to a decrease in IL-6 and IFN production. Moreover, this probiotic strain exhibited the potential to dramatically reduce the clinical signs and symptom. The combination of B. animalis ssp. Lactis and L. reuteri indicated the strongest antiviral activity against respiratory system microbes. L. rhamnosus GG is the most extensively researched probiotic, with substantial reductions in diarrhea length and rotavirus pathogenicity [56].

The COVID-19 disease affects the lungs and the gastrointestinal tract, inducing pro-inflammatory Th1-cells to release various cytokines such as TNF-alpha leading to the establishment of the cytokine storm. Dysregulation in the intestinal microbiome contributes to an imbalance of Th1 and Th2, which stimulates the formation of pro-inflammatory cytokines and, eventually, a cytokine storm in epithelial cells in the lungs [57]. Probiotics promote the proliferation of “beneficial bacteria” in the intestine, resulting in a change in the stability of Th1/Th2 cells, which lowers the cytokine storm and the severity of infections. It was recently found that using probiotic bacteria derived from Lactobacillus and Bifidobacterium improves the chance of healing from COVID-19 patients. L. paracasei and L. coryniformis has the ability to bind angiotensin converting enzyme type 2, which is a receptor needed by the SARS-CoV-2 virus for attachment, preventing its entrance into cell and thereby decrease the possibility of COVID-19 infection [58].


7. Role of probiotics as antifungal

The global fungal load is extremely high, and it is expected to rise even higher as the proportion of immunocompromised people rises. In contrast, the drugs used to treat fungal pollutions are extremely small, and some of them are extremely dangerous. Candida gullemondii, C. auris, C. glabrata, Aspergillus and Fusarium species are evolving as impervious and hazardous fungal pathogens. These species are responsible for 5–10% of global food spoilage [59].

Aflatoxin is an extremely hepatotoxic bioactive compound produced by fungi, which is a major global concern. A toxin-free feed is demanded by the existing agriculture and livestock production industries. Use of such microbes to food preservation has grown in popularity in recent years, owing to customer needs for less reliance on chemical preservatives. Lactic acid bacteria are widely regarded as a “beneficial organism,” that is used to avoid contamination of food and feed, as well as to chemically store food. It is also intended to produce antimicrobial agents [60].

L. fermentum L23 and L. rhamnosus L60 produced bioactive compounds such as hydrolytic enzymes, organic acids, bacteriocins, and hydrogen peroxide and blocked the fungal growth of most all aflatoxigenic strains. L60 has decreased Aflatoxin B1 output by greater than 90 percent and L23 by up to 100 percent. As a result, L23 and L60 have been used to properly manage aflatoxigenic fungi in livestock feed [61].

Probiotics have been shown to decrease C. albicans infections in a variety of body organ systems and are widely regarded as important for good health. Probiotics, for example, can treat gastroenteritis, dairy allergy, and the signs and symptoms of irritable bowel syndrome. C. albicans has been assigned two virulent functions: filamentation and biofilm growth. We can minimize both of these virulent functions through using probiotics. The yeast form of candida is more readily phagocytized than the hyphal form, and probiotics help the host organism combat pathogens by preventing filamentation. However, the exact mechanisms by which fungal infections are prevented are unknown [62].


8. Conclusion

Nowadays, the discovery of the use of probiotic strains has improved our understanding of the relationship between diet and people’s health. Probiotics boost innate and humoral immunity against pathogens. Probiotic bacteria bind to gut epithelial cells and release cytokines (IFN-γ) and interleukins (IL-10) that establish a microclimate in the tracheae, bronchi, and reproductive organs and gut lamina propria, triggering clonal proliferation of B cells to make IgA and activating Treg cells, thereby maintaining immune balance in the gastrointestinal tract. COVID-19 is a newly emerging virus that causes deadly disease all over the world. Probiotic strains, especially lactobacillus species therapy, may be critical in controlling COVID-19, and probiotic treatment may be considered as a choice for the reduction and mitigation of COVID-19 infection globally.


Conflict of interest

The authors declare no conflict of interest.


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Written By

Faisal Siddique, Kashif Akram, Etab Saleh Alghamdi, Qandeel Arshad and Ayesha Siddique

Submitted: May 19th, 2021 Reviewed: June 11th, 2021 Published: April 6th, 2022