CD28 and rheumatoid arthritis: CD28 is a molecule constitutively expressed at the cell surface; thus, the presence of T lymphocytes subsets deficiency in CD28 expression is associated with autoimmune diseases, such as multiple sclerosis, type 1 diabetes, Graves’ disease, ankylosing spondylitis, and RA.24 We found almost 100% of the CD4 + T cells expressing CD28 in RA patients and CS, but no differences were observed among groups.