Patients with systemic lupus erythematosus display heterogeneous immune cell abnormalities that are now being understood in terms of the underlying molecular defects. The fraction of T cells that are involved in the pathogenesis of the disease is characterized in terms of T cell receptor expression, production of inappropriate quantities of lymphokines, and ability to provide help to B cells to produce autoantibodies. The function of antigen-presenting cells is studied in terms of presenting antigens and providing the proper costimulation to T cells. Better understanding of aberrant expression of adhesion molecules may set forward an abnormal tissue response and eventually the expression of clinical disease.