CD28 and systemic lupus erythematosus: The MC10 (CD27+CD28+CD38+CD127−CD197+) and CD4+ central memory (TCM) T-cell (CD45RA−CD197−) subpopulations were the highest in SLE (HCs: 0.648%; RA: 1.040%; SSc: 1.049%; SLE: 1.634%).