CD4 and type 1 diabetes mellitus: Infiltration and activation of several types of innate immune cells in the islets, including macrophages, neutrophils, natural killer (NK) cells, and dendritic cells (DCs), occur at the initial stage of type 1 diabetes and are the major contributor to the establishment of inflammatory milieu in the islets, which is prerequisite for subsequent β cell death and augmentation of the adaptive immune effector response of islet-specific autoreactive CD4+ T cells and cytotoxic CD8+ T cells (2, 3).