Effect of <em>Staphylococcus aureus</em> Cowan I bacteria on the mitogenic response of human B-cell subsets.

We have made a detailed investigation to determine which of the B-cell subsets could be stimulated by Staphylococcus aureus Cowan 1 bacterium (SpA CoI). B-cell subsets were separated from peripheral blood and tonsil lymphocytes by means of rosette formation with E, EA_IgG, anti-immunoglobulin (Ig) conjugated ox erythrocytes (OE-anti-Ig), and Protein A conjugated OE (OE-Pro A) or by separation on a bovine serum albumin (BSA) discontinuous density gradient. The cells responding to SpA Col included E receptor negative (E^-), C3 receptor positive (C3R⁺), and surface Ig positive (SIg⁺) B-cell subsets. Among these B-cell subsets, FcR^- cells were more responsive than FcR⁺ cells. These B-cell subsets responded alone to SpA CoI and significantly proliferated, although they failed to respond alone to pokeweed mitogen (PWM) and Protein A of S. aureus (Protein A). Among the SIg⁺ B-cell subsets stimulated with SpA CoI, IgM⁺ and IgG⁺ B cells showed a marked response and IgA⁺, and IgD⁺ B cells showed much less response. Both Protein A receptor positive (Pro A · R⁺) and negative (Pro A · R^-) cells responded well to SpA CoI. Fractionation of B cells on a BSA gradient revealed that comparatively small sized and denser B-cell subsets responded well to SpA CoI. From these criteria, it is suggested that B cells responding to SpA Col are capable of stimulating not only mature B cells, but can also stimulate immature B cells. [ABSTRACT FROM AUTHOR]