Th2 cell differentiation involves complex changes in expression of multiple genes, many of which have poorly characterized roles. In a gene expression microarray analysis of human primary CD4(+) effector T subsets, we identified that an adaptor protein, GAB2, was preferentially expressed in human Th2 cells. The role of GAB2 in human Th2 cells is unknown. Through analysis of primary and in vitro differentiated human T effector subsets, we confirmed that human Th2 cells preferentially expressed GAB2. Further analysis of public gene expression microarray data of STAT6-knockdowned Th2 cells indicated that GAB2 expression was regulated by IL-4 and STAT6. Both siRNA knockdown and ectopic expression of GAB2 in activated T cells showed that GAB2 positively regulated IL-4 and IL-13 expression in human Th2 cells. We hence identified the adaptor protein, GAB2, as an important novel regulator of the human Th2 immune response.