Profiles of Th1 and Th2 cytokines after primary and secondary infection bySchistosoma mansoni in the semipermissive rat host

In contrast to most mouse strains, rats eliminate the primary schistosome b urden around 4 weeks postinfection and subsequently develop protective immu nity to reinfection. In rat schistosomiasis, we have shown predominant expr ession of a Th2-type cytokine response at the mRNA level after primary infe ction. In the present study, we showed a significant increase in interleuki n-4 (IL-4) mRNA expression in inguinal lymph nodes early after a secondary infection. IL-5 mRNA expression showed a significant increase at days 2 and 4 postreinfection in the spleen and lymph nodes, respectively. We did not detect any gamma interferon (IFN-gamma) mRNA after a challenge infection. A nalysis of cytokine secretion by stimulated spleen cells after a primary in fection showed predominant expression of IL-4 with maximum production on da y 21, accompanied by production of IL-5 from day 11 to day 67. A significan t increase in IFN-gamma secretion was detected at day 21. Analysis of immun oglobulin G2b (IgG2b) and IgG2c (Th1-related isotypes) showed undetectable levels of IgG2b, but detectable levels of specific IgG2c antibodies were ob served from day 42. The analysis of Th2-related isotypes showed high specif ic IgG1 and IgG2a antibody titers from day 29. After a secondary infection, only IL-4 and IL-5 secretion was sustained. This is supported by the incre ased production of Th2-related isotypes. These findings showed that S. mans oni infection can drive Th2 responses in rats in the absence of egg product ion which is required to induce a Th2 response in mice and are in favor of the role of Th2-type cytokines in protective immunity against reinfection.