In vivo expression of cytokine mRNA in rats infected with Schistosoma mansoni

As an animal model, rat schistosomiasis mansoni has provided considerable knowledge of immune mechanisms involved in the expulsion of worms and in a subsequent development of immunity to reinfection. Although it is clear that ADCC mechanisms participate in immunity to reinfection; the nature of the cytokines involved in immunity is unknown. To analyse the pattern of cytokines involved, the mRNA levels of different cytokines were assessed by RT-PCR as they occur within tissues during the course of infection. In spleens from infected rats, a significant elevation in IL-2 and IL-5 mRNA was observed during the early phase of infection (day 7). Analysis of pulmonary cytokine responses showed a dramatic increase in IL-4 and IL-5 on day 7. This was accompanied with a low but significant increase in IL-2 (day 11) and IL-12 (day 7) in the absence of augmented IFN-γ expression. The cytokine expression patterns of draining lymph nodes (LN) from infected rats showed a significant increase of IL-2, IL-4 and IL-5 on day 21. Analysis of IL-10 expression showed exclusively a significant increase in LN on day 11. IFN-γ mRNA was not detected in any tissue sample. Thus, rats develop a predominately Th2-type cytokine response during a primary infection which may be involved at least in part, in the expression of immunity against Schistosoma mansoni infection.