Parasites infections remain a major cause of morbidity and mortality, especially in developing countries while excellent drugs are available to treat many relatively expensive and/or difficult to administer systematically in situations where so many other vital needs compete for limited resources.
The absence of vaccines, the amenability of several mouse models of parasitic infection to experimental analysis, the suitability of parasites infection for studying the immunobiology of chronic infection and of Th2 response development, infection and of TH2 response development, the possibility of molecular cross-talk between helminthes and the mammalian immune system, and the developing realization that parasitic infections affect the ability of an individual to mount immune responses against other Ag (self or non self) make the immunology of parasitic infection an important, challenging, and exciting choice for investigation.
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Immunology is the branch of medicine that deals with the structure and function of the immune system, innate and acquired immunity, the bodily distinction of self from nonself, and laboratory techniques involving the interaction of antigens with specific antibodies.
IMMUNE RESPONSE TO PARASITIC INFECTIONS
Many parasitic diseases are an important cause of mortality and morbidity in humans the resurgence of malaria and trypanosomiasis in countries where these diseases have been effectively controlled and the global increase of several other parasitic diseases, such as cryptosporidiosis and trichinosis are major health problems.
The WHO special programme for research and training of tropical diseases includes seven parasitic diseases:
- African Trypanosomiasis
- Chagas disease
- Lymphatic filariasis
- Onchocerciasis and one vector borne viral disease (dengue) among ten major infectious diseases in its current disease portfolio.
Inspite of every effort made to get vaccine and great importance of these pathogens and the considerable efforts made to develop vaccine against parasitic infections, at present there are no licensed vaccines or immuno therapies for these human diseases.
This is in part due to genetic and antigenic complexity of these organisms, and their ability to evade the immune response, which is often not completely efficient in parasite elimination.
However, in recent years much progress has been made in understanding the immune mechanisms controlling the parasitic infections, thus establishing the scientific background required for the design of safe and efficient vaccines against human parasites. This issue summarises recent development in immunoprophylaxis and immunotherapy of major human protozoan diseases and helminths (Brandonisio et al., 1997).
IMMUNOPATHOLOGY In THE STUDY OF IMMUNE
Many parasites infections are long-lived and cause chronic infections the immune response that develops during this time often proceeds to cause pathologic changes that in many helminth infections are the primary cause of disease. A well studied example of this is the granulomatous reaction that sequesters schistosome eggs.
Adult schistosoma mansoni parasite live within the portal vasculature, where female worms lay eggs, that are intended for transmission across the intestinal wall into the gut lumen and from there to the outside of the host. However, because blood flow in the portal system is towards the liver, many of the eggs are carried to that organ where they become lodged in the sinusoids.
Antigens (Ag) released from eggs induce a marked Th2 response that orchestrates the development of granulomatous lesions in the liver (Wynn et al., 1991). IL-13 is a key regulatory cytokine for Th2 cell mediated pulmonary granuloma formation and lgE responses induced by Schistosoma mansoni eggs. J. Immunol. 162.920-930. The host-protective nature of these lesions has been demonstrated by work in a mouse model of infections with the human parasite.
Infected mice that lack CD4 cells are incapable of making granulomas and die due to the toxic effects on hepatocytes of certain egg proteins (4.33) by surrounding the egg, the granuloma essentially segregates it from hepatic tissue and allows continuing liver functions. In the long term, as the eggs die and granulomas resolve, fibrosis can develop. (Cheerer et al., 1999).
IMMUNE AND IMMUNOPATHOLOGY RESPONSE TO PARASITIC INFECTIONS