Analysis of cytokine mRNA expression during primary granuloma formation induced by eggs of Schistosoma mansoni.

Granulomas induced by parasite eggs are the primary lesions in mice infected with Schistosoma mansoni. Temporal analysis of cytokine mRNA expression in lung tissue containing synchronized granulomas demonstrated a Th0-like pattern of lymphokine expression. IFN-gamma, IL-1 beta, and IL-6 were the primary cytokines induced by day 1 in developing lung granulomas initiated by i.v. egg injection. These changes were followed by increases in expression of IL-2, IL-4, and IL-10 mRNA on day 3 and TNF-alpha and IL-5 mRNA on day 6. Nearly all cytokine mRNA reached maximal levels by day 6, which preceded the peak in granuloma size seen on day 14. In vivo treatment of egg-injected mice with either anti-IL-2 or anti-IL-4 antibodies significantly diminished the size of circumoval granulomas in the lungs. Both groups of antibody-treated animals displayed a marked reduction in IL-4 as well as IL-5 mRNA expression, although IFN-gamma and IL-2 mRNA levels were unchanged or slightly increased. These findings confirm previous observations suggesting a role for IL-2 in egg-induced pathology via the generation of Th2-associated responses, and also indicate a primary function for IL-4 in granuloma formation. Analysis of responses after injection of eggs into nude mice demonstrated that only the Th2 cytokines IL-4 and IL-5 are exclusively dependent on T cells for their induction. Taken together, these data suggest that Th2 cells producing IL-4 play a major role in egg granuloma formation, and that the induction and ultimate down-modulation of Th2-like responses may be influenced by non-T-cell-derived cytokines.