CD28 and systemic sclerosis: MC14 (CD27+CD28+CD45RO+CD127+CD183+CD197+) (HCs: 15.719%; RA: 8.301%; SSc: 7.556%; SLE: 5.911%) and MC15 (CD27+CD28+CD45RA+CD127+CD183+CD197+) were the highest in HCs (HCs: 7.087%; RA: 4.167%; SSc: 3.941%; SLE: 5.065%).