B7/BB1 provides an important costimulatory signal for CD3-mediated T lymphocyte proliferation in patients with systemic lupus erythematosus (SLE).

Successful T cell activation via the T cell receptor (TCR)/CD3 complex requires at least one contact-dependent second signal delivered by costimulatory molecules, including the B7/BB1 molecule, that are present on antigen-presenting cells (APC). SLE is characterized by multiple complex lymphocyte abnormalities of undefined molecular origin. It is currently unclear whether an intrinsic defect of T cell or an underlying APC dysfunction is responsible for defective in vitro proliferation of T cells from patients with SLE. We planned the present experiments to ask whether the TCR/CD3-mediated and B7/BB1-costimulated T cell proliferation is normal in these patients. We used enriched T cell populations that were stimulated with an anti-CD3 MoAb in the presence of controlled quantities of functional B7/BB1 antigen. Freshly isolated T cells from 17 SLE patients (10 and seven patients with either active or inactive disease, respectively) and 11 normal individuals were cocultured with irradiated B7/BB1-transfected P815 cells or parental P815 cells in the presence of OKT3 MoAb at optimal and suboptimal concentrations for 2.5-7 days. Normal or SLE T cells responded similarly to stimulation via anti-CD3, in the absence of B7/BB1 antigen. A several-fold increase in T cell proliferation in the presence of B7/BB1 antigen was observed. Proliferation was inhibited in the presence of anti-B7/BB1 MoAb, but not with control MoAbs. Interestingly, dose-response curves and time kinetics of B7/BB1 costimulation were similar in T cells from patients with either active or inactive SLE at the time of study, and normal individuals. In addition, no differences in the IL-2 receptor release by T cells cultured under these conditions were observed between SLE patients and normal individuals. These results demonstrate that CD28 signalling is not intrinsically impaired in patients with SLE; further studies to investigate whether abnormal B7/BB1 expression is involved in the autoimmune process are needed.