CD28 and systemic lupus erythematosus: Expression of the costimulatory molecule CD28 was measured in six CD4+ and seven CD8+ TCCs from SLE patients and in five TCCs from healthy subjects (Figure 4): while all control TCCs examined (four CD4+ and one CD8+) expressed CD28, only three SLE TCCs were CD28+ (two CD4+ and one CD8+ TCC).