Role for interleukin-3 in mast-cell and basophil development and in immunity to parasites

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Abstract
The cytokine interleukin-3 (IL-3), which can be derived from T cells and other sources, is a potentially important link between the immune and haematopoietic systems1. IL-3 may be particularly critical for the development, survival and function of tissue mast cells1,2,3,4,5,6 and blood basophils7,8, which are thought to be important effector cells in immunity to parasites and other immunological responses, such as allergic reactions9. Here we show, using IL-3-deficient mice10, that IL-3 is not essential for the generation of mast cells or basophils under physiological conditions, but that it does contribute to increased numbers of tissue mast cells, enhanced basophil production, and immunity in mice infected with the nematode Stronglyoides venezuelensis. Parasite expulsion and mast-cell development are impaired even more severely in IL-3-deficient mice that also show a marked reduction in signalling by c-kit. These findings establish a role for IL-3 in immunity to parasites and indicate that one of the functions of IL-3 in host defence against infection is to expand populations of haematopoietic effector cells.