One effector memory (TEM) T-cell (CD45RA−/CD197−) subpopulation, MC08 (CD4+/CD27+/CD28+/CD38−/CD127−/CD197−), was the lowest in HCs and the highest in SLE (HCs: 1.797%; RA: 3.156%; SSc: 3.320%; SLE: 5.396%). Here, CD28 is linked to rheumatoid arthritis.