By comparing SPF, GF, and AF mice that lack exogenous antigens derived from gut microbiota and diet, we report here that dietary antigens effectively induce the majority of conventional IELs, including TCRαβ+ CD8αβ+, TCRαβ+ CD8α+ CD4+, and TCRαβ+ CD4+ IELs. This evidence concerns the gene CD4 and atrial fibrillation.