To characterize Th cell populations induced by helminth
infection, spleen cells from mice infected with Schistosoma mansoni were stimulated with parasite (worm or egg Ag) or
mitogen (Con A) and the supernatants assayed for the Th1-specific
cytokines IFN-gamma and
IL-2 and the Th2-specific
cytokines IL-4 and
IL-5. Th2
cytokine production was not detected in substantial quantity until the 6 to 8th wk of
infection and after reaching peak levels at 8 to 12 wk declined slowly thereafter. The time courses of
IL-4 and
IL-5 production, whereas differing from each other, closely resembled corresponding published data on
IgE and peripheral blood eosinophil levels during murine schistosome
infection. In contrast, Th1
cytokine responses occurred only during the first 6 wk of
infection and were virtually absent during the peak period of Th2 production. To assess the role of egg deposition in the observed pattern of Th response,
cytokine production was assayed in mice carrying unisexual schistosome
infections in which parasite eggs are absent. Splenocytes from these animals displayed only marginal Th2
cytokine synthesis but greater Th1
cytokine responses than the corresponding cells from mice with bisexual
infections. Moreover, cultures of liver tissue or isolated
granulomas from infected mice constitutively produced high levels of
IL-4 and
IL-5 but failed to synthesize significant amounts of
IL-2 and IFN-gamma even when stimulated with egg Ag or
mitogen. Taken together the data indicate that egg deposition is the major stimulus of Th2
cytokine response in S. mansoni-infected mice and suggest that T cells belonging to this subset must play a major role in egg
granuloma formation.