IL-1 causes a marked increase in the degree of expansion of naïve and memory CD4 T cells in response to challenge with their cognate antigen. The response occurs when only specific CD4 T cells can respond to IL-1β, is not induced by a series of other cytokines and does not depend on IL-6 or CD-28. When WT cells are primed in IL-1R1^−/− recipients, IL-1 increases the proportion of cytokine-producing transgenic CD4 T cells, especially IL-17- and IL-4-producing cells, strikingly increases serum IgE levels and serum IgG1 levels. IL-1β enhances antigen-mediated expansion of in vitro primed Th1, Th2, and Th17 cells transferred to IL-1R1^−/− recipients. The IL-1 receptor antagonist diminished responses to antigen plus lipopolysaccharide (LPS) by ≈55%. These results indicate that IL-1β signaling in T cells markedly induces robust and durable primary and secondary CD4 responses.