CD28 and autoimmune disease: Unlike the cytotoxic role exerted by CD4 + CD28 null T cells described in RA, a regulatory behavior of CD8 + CD28 − T cells has been identified in infections, cancer, and autoimmune diseases.27 These lymphocytes are able to inhibit a Th1‐type response,28, 29, 30 which has a pivotal role to maintain a proinflammatory microenvironment in RA.