Immune response to Anisakis simplex and other ascarid nematodes

Anisakis simplex is a nematode parasite belonging to the Ascaroidea group, which includes several species of medical importance, and the immune response to A. simplex is discussed with reference to some of these. The strong Th2 reaction usually provoked by nematodes seems to occur only in the context of infection, and exposure to nonviable antigens fails to do so. This would imply either that allergic reactions to A. simplex require prior infection, or that a classical atopic response is responsible, and the cause possibly varies among patients. The antibody response to secreted and exposed surface antigens of if. simplex is strong, and should be explored as potentially a better antigen source for serodiagnosis than somatic materials, and it might also be useful in addressing the question of the role of infection in predisposing to allergic reactions. As in toxocariasis, both secreted and shed surface antigens of A. simplex could provide a focus for inflammatory lesions in tissue-invasive larvae. Humans respond heterogeneously to A. simplex allergens, and experience with other nematodes would indicate that this is due to genetic control of the immune repertoire by the major histocompatibility complex, a fact which, in turn, might have clinical implications. A. simplex is known to produce allergens similar to the ABA-1 of Ascaris, which represents a structurally novel class of fatty acid and vitamin A-binding protein. This and other recently described nematode proteins are known to be highly stable to thermal denaturation and can recover their structures, biochemical activities, and allergenicity upon cooling.