The IL-1 family members IL-1ß, IL-18, and IL-33 are potent cytokines in relationship to amplifying the CD4(+) T cell cytokine production. To evaluate their impact on in vitro-differentiated human Th1 and Th2 cultures, such cultures were established from naive T cells, purified from healthy blood donors, and reactivated in the presence of IL-1ß, IL-18, or IL-33. Interestingly, we observe modifying responses in Th1 and Th2 cultures induced by IL-18 or IL-33 but not by IL-1ß, both contributing to amplify production of IL-5, IL-13, and IFN-¿. IL-18 or IL-33 stimulation of Th1 cultures resulted in increased IFN-¿ and IL-13 production concurrent with reduced IL-10 gene transcription and secretion even though Th1 cultures, in contrast to IL-18Ra, had low ST2L expression. Furthermore, adding IL-18 to Th1 cultures promoted Tbet mRNA expression and production. Th2 cultures stimulated with IL-18 or IL-33 had an increased IL-5 secretion. Interestingly, E4BP4 gene expression and the percentage of E4BP4(+) cells of the recently shown IL-10 transcriptional regulator E4BP4 correlated with IL-10 gene expression and protein secretion in Th1 cultures. Taken together, we report that the IL-1 family "alarmins" IL-18 and IL-33 in addition to amplifying both Th1- and Th2-associated cytokines block production of the regulatory cytokine IL-10 in Th1 cultures.