CD4 and diabetes mellitus: The immune system plays an essential role in the pathogenesis of diabetes: the insufficient central tolerance of thymus, too little variable number of tandem repeats (VNTR), quantitative and quality defects in Tregs lead to CD8+T cells attacking islet β cells, while inflammatory cytokines and recruitment of macrophages, B cells and CD4+T cells assist in attacking islet β cells, resulting in insufficient insulin secretion (Donath et al., 2019; Chen et al., 2021; Petrelli et al., 2021; Roep et al., 2021).