CD5+ B lymphocytes in systemic lupus erythematosus and rheumatoid arthritis.

B lymphocytes which express the CD5 antigen on their cell surface have the ability to produce autoantibodies in vitro. We describe 2 patients, one with systemic lupus erythematosus and another with rheumatoid arthritis, whose percentages of peripheral blood CD5+ B lymphocytes were dramatically increased to 68 and 100%, respectively. A reduction of this subpopulation of B cells was associated with clinical improvement after therapy. This association suggests a relationship between CD5+ B cells and autoimmune disease activity.