Schistosoma mansoni infection in mice augments the capacity for interleukin 3 (IL-3) and IL-9 production and concurrently enlarges progenitor pools for mast cells and granulocytes-macrophages.

Mast cells and granulocytes-macrophages (GM) are components of the host defense system against worm infections, including schistosomiasis. Here we report the kinetics of changes in the number of colony-forming cells (CFC) for mast cells and GM during the course of a primary experimental infection of mice with Schistosoma mansoni cercariae over a period of 24 weeks postinfection (p.i.). Concurrently, we measured known myelopoietic and/or mast cell-stimulating cytokines (i.e., interleukin 3 [IL-3] and IL-9) in pokeweed mitogen-activated spleen cell-conditioned medium. Our results show that during the acute phase of the hepatic granulomatous reaction, the numbers of both mast-CFC and GM-CFC were significantly elevated in bone marrow. However, while femoral GM-CFC numbers had returned to normal control values at week 16 p.i., femoral and splenic mast-CFC numbers remained significantly elevated until week 20 p.i., which corresponds to the chronic fibrotic phase of hepatic granulomatous inflammation. Increased GM-CFC numbers correlated with elevated IL-3 levels, while increased mast-CFC numbers paralleled the increased IL-9 concentrations in spleen cell-conditioned medium. By the reverse transcription-PCR method, enhanced expression of IL-3 and IL-9 transcripts was found in RNA samples obtained from livers and spleens of infected mice. Our data demonstrate that during the course of infection of mice with S. mansoni, the coordinate need for mast cells and GM is at least partly regulated at the stage of progenitor cell commitment in the bone marrow and spleen. It appears that IL-3 and IL-9 help to promote at this stage the ultimate generation of mature effector cells.