Distinction of two subtypes of human leukocyte interferon (IFN-alpha) on B cell activation. B cell proliferation by two subtypes of IFN-alpha.

We examined the effect of interferon (IFN), with particular emphasis on the effects of the two subtypes of IFN-alpha (IFN-alpha A and IFN-alpha B) on the B cell proliferation induced by Staphylococcus aureus Cowan I bacterium (SpA Col). An increase of SpA Col-induced proliferation was observed in the presence of 100 to 1000 U/ml of IFN-alpha, but a decrease of SpA Col-induced proliferation was observed in the presence of 1000 to 10,000 U/ml of IFN-beta. The two subtypes of IFN-alpha had different effects on cell proliferation; a significant enhancement was shown in the presence of 1000 to 10,000 U/ml of IFN-alpha A, but inhibition was shown in the presence of 1000 to 10,000 U/ml of IFN-alpha B. In the reconstitution test of the two subtypes of IFN-alpha, the boundary between enhancement and inhibition of SpA Col-induced proliferation was revealed when the proportion of IFN-alpha A and IFN-alpha B (IFN-alpha A:IFN-alpha B) ranged between 8:2 and 9:1. Toward the SpA Col-induced responses, the above IFN were all found to act on B cells directly, independent of the presence of T cells. Proliferative responses by IFN-alpha and IFN-alpha A, however, were shown to be slightly dependent on the presence of monocytes. The lymphocyte proliferation induced by other mitogens (phytohemagglutinin, concanavalin A, pokeweed mitogen, and protein A of S. aureus) were all inhibited by the above IFN.