In response to an acute viral infection, activated virus-specific CD4+ T cells differentiate into either TH1 or TFH cells.15,55,56 We first adoptively transferred LCMV-specific naïve SMARTA cells (expressing a transgenic T cell receptor specific for the LCMV glycoprotein epitope I-AbGP66–77) into WT C57BL/6J recipients and subsequently infected the chimeric recipients with the LCMV Armstrong strain to investigate the potential regulatory regions involved in this bifurcated differentiation at the genome level. This evidence concerns the gene CD4 and viral infectious disease.