Schistosoma mansoni infection induces a type 1 CD8+ cell response.

We have found that infection with the large extracellular parasite S. mansoni leads to the development of a type 1 CD8+ T cell response. While there are many poorly understood aspects of this immune response, our working hypothesis is that it functions primarily to regulate the parasite egg-antigen induced Th2 response, which itself is responsible for circumoval granunuloma formation. This view of the activity of CD8+ cells mirrors Bloom and colleagues' postulate that type 2 CD8+ cells function to regulate Th1 responses. Since it is well recognized that Th1 and Th2 cells can cross regulate each other, why should a type 1 CD8+ rather than a Th1 response be used for the regulation of the Th2 response during schistosomiasis? The answer to this may in part lie in the apparent dependence of the type 1 CD8+ cells on IL-4. Because of this, there is little likelihood for the over-production of IFN-gamma (a potentially dangerous proinflammatory cytokine) and "suppression" is provided only when needed. Th1 cells have no such dependence on IL-4 for IFN-gamma production. Current work in the laboratory is directed towards testing the various hypotheses put forward here.