SpA-induced immunoglobulin production in human peripheral blood lymphocytes. I. Conditions of SpA-induced immunoglobulin production.

Protein A (SpA) is a component of the cell wall of Slop,lylococcus aureers. SpA is unique in that it combines with the Fc portion of immunolgobulins from many speciesi,2) and has been used in immunochemical studies3,`>. Another distinctive f ature of SpA is its potent mitogenic activity on lymphocytes from several species, including hurnans5,iO}. SpA also exerts a mitogenic activity on both T and B cells 6,8,iO}. Moreover, SpA is a striking contrast to other polyclonal B cell activators (PBAs) because it combines with the Fc portion of immunoglobulins. It is thus likely that SpA reacts with cell surface immunoglobulin receptors and in turn delivers