Protein A-activated rat splenic lymphocyte proliferation involves tyrosine kinase-phospholipase C-protein kinase C pathway

Protein A (PA) of Staphylococcus aureus was long been known for its affinity towards the Fc domain of immunoglobulin G. It is now well established that PA is a potent biological response modifier showing simultaneously antitumor, antitoxic, and anticarcinogenic properties. This bacterial protein was also observed to stimulate production of cytokines. But the molecular mechanism(s) of immunocyte activation by PA still remained essentially unknown. In this report, we demonstrate a hitherto undescribed role of PA as a signal inducer in rat splenic lymphocytes. Our studies describe that PA induces transition of G0/G1 to S and G2/M phases of cell cycle, thus ultimately stimulating splenic lymphocyte proliferation. It has also been revealed that PA binds to rat splenic lymphocytes in a dose dependent manner and stimulates proliferation via tyrosine kinase-phospholipase C (PLC)-Ca2+-dependent protein kinase C (PKC) pathway. These observations will be of valid help in correlating the immunostimulatory activities of PA with the molecular mechanism(s) of its action.