Staphylococcus aureus Wood 46 strain activates human B cells without affecting DNA synthesis or tyrosine phosphorylation.

Induction of Ig secretion in human tonsilar B cell by protein A-deficient Staphylococcus aureus WOOD 46 strain (SAW) was examined. SAW induced as much Ig secretion as protein A-rich S. aureus Cowan I strain (SAC) when IL-2 was present in the culture. Activated and resting B cells are separated by Percoll gradient to determine whether SAW stimulates either resting or activated B cells. In resting B cells, SAW plus IL-2 induced IgM secretion significantly, but neither IL-2 nor SAW alone induced IgM secretion. In activated B cells, however, IL-2 induced IgM secretion by itself and SAW plus IL-2 did not induce additional IgM secretion. These results suggest that SAW activates small resting B cells rather than preactivated B cells. Subsequently, mechanisms of B cell activation by SAW and SAC were compared. SAW did not induce [3H]-TdR incorporation through day 1 to 5, and the number of viable cells was not increased by SAW stimulation. Moreover, SAW did not induce significant tyrosine phosphorylation at any concentration tested, when tyrosine phosphorylation of B cells was examined. However, SAC induced both [3H]-TdR incorporation and tyrosine phosphorylation of B cell efficiently. In further experiments, induction of IL-2R and IgM mRNA expressions were examined. SAW by itself induced IL-2R and IgM mRNA expressions without affecting expression of membrane-type IgM mRNA. These results show that SAW activates human B cells in quite a different manner from SAC by up-regulating the expression of secretory type IgM mRNA without affecting cell proliferation nor tyrosine phosphorylation, proposing a distinct B cell activation model from SAC.