IL-18, although antiallergic when administered with IL-12, stimulates IL-4and histamine release by basophils

IL-18 is a proinflammatory cytokine that plays an important role in natural killer cell activation and T helper 1 (Th1) cell responses. Mast cells and basophils are major inducers and effecters of allergic inflammation. Here we show that basophils and mast cells derived by culture of bone marrow cel ls with IL-3 for 10 days express IL-18R alpha chain and that basophils prod uce large amounts of IL-4 and IL-13 in response to stimulation with IL-3 an d IL-18. Injection of IL-12 and IL-18 inhibits IgE production in helminth-i nfected wildtype mice and abolishes the capacity of their basophils to prod uce IL-4 and IL-13 in response to stimulation either with IL-3 and IL-18 or with Fc is an element of R cross-linkage, By contrast, this combination of cytokines actually increases IgE levels in helminth-infected IFN-gamma(-/- )mice and enhances IL-4 and IL-13 production by their basophils. Furthermor e, injection of IL-18 alone enhances basophil production of IL-4 and histam ine both in wild-type and IFN-gamma(-/-) mice. Thus, IL-18 has the potentia l to stimulate basophils but, when given with IL-12, exhibits an antiallerg ic action in vivo.