Central role for interleukin-4 in regulating nitric oxide-mediated inhibition of T-cell proliferation and gamma interferon production in schistosomiasis

Schistosoma mansoni-infected wild-type (WT) mice develop a Th2 response and chronic disease. In contrast, infected interleukin-4 double-deficient (IL-4^-/-) mice develop a Th1-like response and an acute, lethal syndrome. Disease severity in these animals correlates with excessive and prolonged production of nitric oxide (NO) associated with enhanced antigen-driven gamma interferon (IFN-γ) production in the absence of IL-4. Strikingly, splenic lymphocytes from infected IL-4^-/- mice failed to proliferate as well as those from infected WT mice following stimulation in vitro with antigen or anti-CD3 antibody. Contrary to antigen-driven IFN-γ responses, anti-CD3 antibody stimulation of splenocytes resulted in significantly less IFN-γ being produced by CD8 cells from infected IL-4^-/- mice than by those from infected WT mice or normal mice. NO is largely responsible for the impaired T-cell functions in infected IL-4^-/- mice, as inhibition of iNOS significantly enhanced proliferation and IFN-γ production.