Protozoan and Helminth Parasites
Macrophages are one of the main phagocytic cells capable of destroying parasites. Once the parasite is ingested by these cells, they begin to produce nitric oxide (NO), a potent chemical that is toxic to these pathogens. In fact, NO related products are toxic to malaria, leishmania, trypanosomes, shistosome larvae. interferon-gamma (IFN-γ) activates the macrophage that produces the NO (Figure 3).
Antigens of many intracellular parasites are processed and presented via the endogenous antigen-presenting pathway. This involves ingesting the parasite, digestion within the phagocyte's cytoplasm, and presenting using MHC class I molecules. Antigens presented by MHC class I molecules become targets for cytotoxic T lymphocytes (CTL). CTL like their targets by inserting perforin protein into the cell membrane of the infected cell presenting the parasitic antigen, essentially creating a pore-like hole in the membrane. The CTL then releasing granzymes (specialized digestive enzymes) into the infected cell, which induces apoptosis to occur shortly after. The CTL detaches from its target and goes to look for another infected cell (Figure 4).
Antibodies: Important for some protozoa's and helminths that infect the gut (Figure 5).
Mast cells and goblet cells for intestinal parasites. Mast cells release toxic mediators, while mucin secretions by goblet cells prevents nutrient uptake by the parasite and may aid in flushing out the parasite. IL-4 may also induce gut motility.
Eosinophils are important for destroying larval stages of helminth parasites.
The following is a list of parasites that have been profiled:
click the animation to read more about the featured organism