CD28 and rheumatoid arthritis: MC06 (CD27+CD28+CD38−CD57+CD127−HLA-DR−) differed from MC01 and MC05 in terms of CD27+CD28+ and CD38−CD127− and showed the highest prevalence in HCs (HCs: 2.492%; RA: 1.083%; SSc: 0.921%; SLE: 0.910%) (Figure 5B; Supplementary Figure 13B).