Immunological events during the early phase of infection with Schistosoma mansoni in mice

Naturally occurring infection in humans or experimental infection in mice by Schistosoma mansoni lead to a Th1 towards Th2 switch of cytokine response in the chronic late phase of the disease, It has been proposed that an initial Th1 response is successively down-regulated and followed by an egg-antigen driven Th2 response, Here we report the results of a kinetic study on the capacity of spleen cells from experimentally infected Balb/c mice to produce Th1 or Th2 cytokines, following mitogen stimulation, during the phase which precedes the granulomatous response associated to egg-deposition, The main results were identified as an early increase in IL,-4 and IL-10 Th2 cytokine production, particularly pronounced for IL-10, only a slight and delayed decrease in IL,-2 production and an invariable or actually enhanced capacity to produce IFN-gamma, The emergence of Th2 response was associated with only slight and delayed modifications in spleen lymphocytesubsets, mainly represented by a decrease in CD3+ T cells and an increase in B cells, The initial unbalance of the Th1/Th2 response precedes thus the egg-deposition and the chronic phase of the infection, being evident 3 weeks after the challenge with the parasite, This observation could represent a novel finding useful in understanding the complex mechanisms involved in the immunopathogenesis of schistosomiasis.