Evidence of GATA‐3‐dependent Th2 commitment during the in vivo immune response

The transcription factor GATA-3 has been shown to play an important role for the in vitro induction of Th2 cells. To clarify how the in vivo immune response is governed under GATA-3 function, we generated double-transgenic mice by crossing GATA-3 transgenic mice with ovalbumin (OVA)specific TCR transgenic mice. After immunization with OVA, the double-transgenic mice showed increased expression of GATA-3 in antigen-reactive fresh CD4 + T cells, and higher production of IL-5 and IL-13 in cultured spleen cells in the presence of cognate antigen without any polarizing conditions for Th2 cells. Moreover, the immunized double-transgenic mice showed a higher increase of in vivo secretion of IL-5 and IL-13 in bronchoalveolar lavage fluid after OVA aerosol challenging. The serum levels of OVA-specific IgG1, IgE and IgA antibodies were much higher in the immunized double-transgenic mice than TCR transgenic mice. These findings provide direct evidence that antigen-stimulated CD4 + T cells in the immunized mice have already been committed into Th2 cells producing IL-5 and IL-13 selectively through enhanced GATA-3 expression in vivo, thereby inducing higher production of antigen-specific antibody for three isotypes other than IgM.