Elimination of lymphocytes, but not eosinophils, by Fas-mediated apoptosisin murine schistosomiasis

Infection with the helminth parasite Schistosoma mansoni is associated with a pathogenic granulomatous response to parasite eggs. Multiple cell types constitute the granuloma with eosinophils achieving numerical dominance. We hypothesize that eosinophil dominance is achieved by selective apoptosis i n lymphocytes. We report here that lymphocytes from both the spleens and gr anulomas of S. mansoni-infected mice undergo apoptosis. We also show that g ranuloma lymphocytes are more susceptible to Fas-FasL-mediated apoptosis th an spleen lymphocytes and this apoptosis may be related to antigen concentr ation. Conversely, eosinophils from the granuloma and spleens of S. mansoni -infected mice are resistant to apoptosis in vivo and are protected in vitr o from Fas-FasL-mediated apoptosis by the absence of FasL expression in the presence of Fas expression. Finally, the apoptotic regulatory molecules Bc l-2, Bcl-xL, and Bax, do not appear to play a significant role in the regul ation of eosinophil apoptosis in the schistosome granuloma.