Effect of Staphylococcus aureus 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 I bacterium (SpA CoI). B-cell subsets were separated from peripheral blood and tonsil lymphocytes by means of rosette formation with E, EAIgG, anti-immunoglobulin (Ig) conjugated OE (OE-Pro A) or by separation on a bovine serum albumin (BSA) discontinuous density gradient. The cells responding to SpA CoI included E receptor negative (E-), C3 receptor positive (C3R+), and surface Ig positive (SIg+) B-cell subsets. Among these B-cell subsets, FcR-n 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 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 CoI are capable of stimulating not only mature B cells, but can also stimulate immature B cells.