Induction of immunoglobulin secretion by protein A from Staphylococcus aureus in human blood and bone marrow B cells.

Antibody secretion was measured in vitro as plaque-forming cells (PFC), using an indirect haemolysis-in-gel assay. Protein A from Staphylococcus aureus (SPA) induced 4900 +/- 1800 (mean +/- SE from 12 individuals) IgG+A+M PFC/10(6) blood lymphocytes. This was comparable to responses induced by Staph. aureus Cowan 1, lipopolysaccharide, pokeweed mitogen, and purified protein derivative of tuberculin. In bone marrow, SPA induced the highest number of PFC (36,500 +/- 100/10(6) of all the B-cell activators. SPA mainly induced IgG PFC and only a few IgA and IgM PFC. In blood, B cells enriched by sheep erythrocyte sedimentation gave a higher PFC response to SPA than unseparated blood lymphocytes, whereas almost no stimulation was seen in enriched T cells. In bone marrow, the highest number of PFC stimulated by SPA was often seen among the enriched T cells. After the removal of adherent and phagocytic cells, the number of PFC induced by SPA was reduced in blood and bone marrow cells. In enriched B cells from blood, the number of PFC stimulated by SPA increased in the presence of enriched T cells depleted of OKT8-positive cells and decreased when cultured with T cells depleted of OKT4-positive cells. It is concluded that macrophages/monocytes and T helper and suppressor cells play a role in the regulation of human B-cell antibody secretion induced by SPA.