Abstract
Abnormalities in the regulation of both cell-mediated and humoral immunity have been implicated in the pathophysiology of systemic lupus erythematosus (SLE). Cognate contact-dependent T-B cell interactions involving CD154 (CD40 ligand) on activated T cells and CD40 on B lymphocytes have a critical role in antibody production. Abnormal CD154 expression on lymphocytes may play a role in the production of potentially pathogenic autoantibodies and defects in self-tolerance mechanisms may be important. Failure of intrathymic or peripheral deletion of autoreactive T cells may also result in an autoimmune phenotype. Elevated levels of CD3(+)CD4(-)/8(-) (double negative) T cells (DNT) in the peripheral blood are a surrogate marker for defects of this type. The expression of CD154 on T and B cells was evaluated and levels of double negative T cells in the peripheral blood were assessed by two and three colour flow cytometric analyses. We studied peripheral blood lymphocytes in 48 patients with SLE. Twenty-five normal subjects and 12 patients with rheumatoid arthritis (RA) were studied as disease controls. T cells in 22/48 (45%) lupus patients expressed CD154 between 20-80% (median=52%). In normal controls and RA patients 8-18% T cells were CD154(+). Twelve patients (30%) had elevated expression of CD154 (20-50%) on B cells. In the control RA patients, less than 15% T cells were CD154(+). Twelve of 48 SLE patients had elevated numbers of DNT cells (18-27%). The control subjects had DNT cell numbers <10. These observations suggest that defects in either the intrathymic or peripheral deletion of potentially pathogenic T lymphocytes may play a role in the pathogenesis of SLE. The high expression of CD154 on both T and B cells may also be important in mediating the production of potentially harmful autoantibodies.