IL-3 is required for increases in blood basophils in nematode infection in mice and can enhance IgE-dependent IL-4 production by basophils in vitro

Basophils represent potential effector and immunoregulatory cells, as well as a potential source of IL-4, during the immune response elicited by infection with the nematode Nippostrongylus brasiliensis ( N.b. ), and in other settings. However, the factors which regulate the numbers of blood basophils in mice, or the ability of these cells to produce IL-4, are not fully understood. We found that infection of mice with the nematodes N.b . or Strongyloides venezuelensis ( S.v. ) induced substantial increases in the numbers of blood basophils (to as high as 18% of circulating blood leukocytes). Experiments in IL-3 −/− vs IL-3 +/+ mice, and in IL-3-treated IL-3 −/− mice, showed that essentially all of the increases in blood or bone marrow basophils during N.b. or S.v . infection were IL-3 dependent. Many of the blood, bone marrow or liver-derived basophils from IL-3 −/− or IL-3 +/+ mice expressed intracellular IL-4 upon stimulation with anti-IgE in vitro . However, after incubation of the cells with exogenous IgE in vitro , blood- or liver-derived basophils from IL-3 +/+ mice exhibited higher levels of intracellular IL-4 after stimulation with anti-IgE than did basophils derived from IL-3 −/− mice. Thus, IL-3 is a major regulator of the marked increases in blood basophil levels observed during infection of mice with N.b . or S.v . and also can enhance levels of intracellular IL-4 upon activation of basophils with anti-IgE in vitro .