CD4 and atrial fibrillation: However, in AF mice, granzyme B production was severely impaired across both conventional (TCRαβ+ CD8αβ+ and TCRαβ+ CD4+ CD8αα+) and unconventional (TCRαβ+ CD8αα+ and TCRγδ+) IELs, indicating that dietary antigens, even if unprocessed by the gut microbiota, are sufficient to induce granzyme B production in IELs (Figures 2A, B).