Leishmania is the causative protozoan parasite of leishmaniasis. Distinct species provoke localized/diffuse cutaneous leishmaniasis or visceral leishmaniasis. Leishmania parasites have developed diverse strategies to evade the host immune response expressed through various cells, especially macrophages, NK cells, and dendritic cells. Participating in some of these strategies are Leishmania surface molecules, such as lipophosphoglycan (LPG) and protease gp63, which are thus considered virulence factors. LPG has been shown to modulate proinflammatory responses. For example, L. major LPG activates NK cells through toll-like receptor-2 (TLR2), while L. mexicana LPG elicits a differential production of cytokines in human dendritic cells and monocytes. Moreover, L. mexicana LPG activates MAP kinases in macrophages, which in turn enhance proinflammatory cytokine production through TLRs. Additionally, Leishmania exosomes have been found to strongly affect macrophage signaling and functions. Furthermore, proteins secreted by Leishmania promastigotes and amastigotes modulate the production of proinflammatory cytokines in human macrophages. Since Leishmania is an obligate intracellular parasite, its promastigotes utilize several mechanisms to survive and duplicate inside host cells, including the inhibition of apoptosis. It is now clear that MAPK p38, JNK, ERK 1/2, and PI3K/Akt participate in the inhibition of both natural and induced apoptosis of macrophages, neutrophils, and dendritic cells.
Part of the book: Leishmaniases as Re-emerging Diseases
Apoptosis is a biological process carried out during maturation, remodeling, growth, and developmental processes in tissues, and also represents an important defense mechanism of cells against intracellular microorganisms. In counterpart, diverse intracellular pathogens have developed a wide array of strategies to evade apoptosis and persist inside cells. Apoptotic cell death can be triggered through different intracellular signaling pathways that lead to morphological changes and eventually cell death. Among these pathways, MAPK and PI3K play a central role. The precise control of the signaling pathways that lead to apoptosis is crucial for the maintenance of tissue homeostasis. Paradoxically, these same pathways are utilized during infection by distinct intracellular microorganisms in order to evade recognition by the immune system, inhibit apoptosis, and therefore survive, reproduce, and develop inside cells.
Part of the book: Current Understanding of Apoptosis
Dendritic cells comprise a complex array of cell populations that play a leading role in immune defense. In an immature state, they have the capacity to sense and uptake different antigens. Upon capturing antigens, they become activated, mature, and migrate to lymph nodes where they present antigen-derived peptides to naïve T cells. Due to these excellent surveillance properties, dendritic cells play an important role against parasitic infections. Also, dendritic cells are an important source of IL-12, which is a fundamental proinflammatory cytokine in the control of intracellular parasites. The aim of this chapter is to review the most important characteristics and functions of dendritic cells and their role in the control of infection by parasites.
Part of the book: Dendritic Cells
Trypanosoma cruzi is an intracellular parasite, which causes Chagas disease, affecting millions of people throughout the world. T. cruzi can invade several cell types, among which macrophages and cardiomyocytes stand out. Chagas disease goes through two stages: acute and chronic. If it becomes chronic, its most severe form is the chagasic chronic cardiomyopathy, which accounts for most of the fatalities due to this disease. For parasites to persist for long enough in cells, they should evade several host immune responses, one of these being apoptosis. Apoptosis is a type of programmed cell death described as a well-ordered and silent collection of steps that inevitably lead cells to a noninflammatory death. Cells respond to infection by initiating their own death to combat the infection. As a result, several intracellular microorganisms have developed different strategies to overcome host cell apoptosis and persist inside cells. It has been shown that T. cruzi has the ability to inhibit host cells apoptosis and can also induce apoptosis of cells that combat the parasite such as cytotoxic T cells. The aim of this chapter is to present up-to-date information about the molecules and mechanisms engaged by T. cruzi to achieve this goal and how the modulation of apoptosis by T. cruzi reflects in the development of chronic chagasic cardiomyopathy.
Part of the book: Chagas Disease