Immunity to Parasites and Apoptosis

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IMMUNITY TO PARASITES AND APOPTOSIS. Humoral and cellular immunity are the two sides of immunity turn on during parasitic infections and ideally are aimed to fight infection. However, in some cases immunity to parasites can exacerbate the disease and induce tissue injury. Cellular Immunity Animal models have been most useful to better understand mechanisms of immunity to parasites. Athymic mice that lack T cells are unable to control several parasite infections. This clearly indicates that T cells play an important role during the development of these infections (39,40). In the introduction of this chapter, we described some general aspects of the immune response, including cellular immunity, here we will try to expand this information. There are two major types of lymphocytes that originate in the bone marrow: B lymphocytes which mature in the bone marrow and after activation they differentiate into plasma cells that secrete antibodies. The second type are known as T lymphocytes which are derived from stem cells in the bone marrow, but mature in the thymus and are further subdivided into two broad types: cytotoxic T lymphocytes (CD8+ T cells) which kill cells infected with viruses o cells that have been transformed into cancer cells, whereas the second class of T cells (CD4+ T cells) are essential in determining B cell antibody class switching and in the activation macrophages and cytotoxic T cells (22). Macrophages are cells originated in the bone marrow and they are one of the three types of phagocytes besides of dendritic cells and neutrophils. Macrophages are distributed throughout the body in different tissues and play an important role in innate immunity. Monocytes differentiate into macrophages upon migration into di... ... middle of paper ... ...s reported in the nephrotic syndrome of quartan malaria, may produce several other pathological conditions (54). Hepatomegaly and splenomegaly of malaria, trypanosomiasis and visceral leishmaniasis are all associated with increased numbers and activity of lymphocytes and macrophages in those tissues (8,53,54). Fibrosis and the enlarged liver in schistosomiasis are a pathologic consequence of granuloma formation surrounding the worm eggs, similar to a delayed type hypersensitivity reaction and can be responsible of the symptomatology in patients with pulmonary schistosomiasis (55) (see chapter 4). Immunosuppression is also frequently found in many diseases such as malaria, Chagas’ disease and diffuse cutaneous leishmaniasis and may lead to concomitant bacterial or viral infections or Burkitt’s lymphoma which is sometimes associated with malaria (8,53,56,57).
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