Impaired B cell proliferation by Staphylococcus aureus Cowan 1 in patients with systemic lupus erythematosus.

We examined the proliferative response to Staphylococcus aureus Cowan 1 (SAC) by enriched peripheral blood B cells from patients with systemic lupus erythematosus (SLE). Responses of B cells from patients with active and inactive SLE were significantly lower than those of B cells from normal individuals. Hyporesponsiveness to SAC was not observed in healthy family members of SLE patients. This hyporesponsiveness did not correlate with prednisolone therapy and could not be attributed to serum factors; it did correlate with the presence of suppressor monocytes. However, we could not exclude the possibility of enhanced sensitivity of SLE B lymphocytes to suppressive signals delivered by the monocytes.