CD28 and autoimmune disease: The features of T cell exhaustion include progressive loss of function, upregulation of inhibitory receptors, altered transcriptional and epigenetic profiles, reduced proliferative capacity, metabolic dysfunction, decreased cytotoxicity, etc. T cells in SLE patients may undergo multiple rounds of activation and proliferation, leading to some T cells losing CD28 expression and becoming CD28 negative effector T cells, a phenomenon common in chronic inflammation and autoimmune diseases.