CD28 and systemic lupus erythematosus: In this study, we find that cytotoxic CD4<sup>+</sup>CD28<sup>-</sup> T cells are expanded in SLE patients with flow cytometry analysis, and the percentage of CD4<sup>+</sup>CD28<sup>-</sup> T cells positively correlates with the Systemic Lupus International Collaborating Clinics/ACR Damage Index (SDI).