Regulation of Human B Cell Responsiveness by Interferon-α: Interferon-α-Mediated Suppression of B Cell Function Is Reversed through Direct Interactions between Monocytes and B Cells

Previous studies have revealed that interferon-α (IFN-α) suppresses the B cell responses stimulated with Staphylococcus aureus (SA) I IL -2 in the complete absence of monocytes but enhances the responses of B cells contaminated with monocytes. The current studies therefore examined in detail the combined effects of IFN-α and monocytes on the B cell responses induced by SA + IL-2. Monocytes overcome the suppressive effects of IFN-α on the IgM production induced by SA I IL -2. Thus, in the presence of monocytes, IFN-α enhanced the IgM production by B cells stimulated with SA I IL-2. IFN-α still enhanced the IgM production induced by SA I IL -2 in the presence of monocytes and indomethacin. The IFN-α-mediated suppression of B cell responsiveness was not overcome by addition of factors generated from SA-activated monocytes, or any of IL-1β,IL-6, and TNF-α. Of note, the IFN-α-mediated suppression of B cell responsiveness was overcome only when B cells and monocytes were allowed to contact with each other. This reversal of the IFN-α-mediated suppression of B cell function was not blocked by any of the mAb to CD11a, CD18, CD54, or monomorphic determinants of HLA-DR. These results indicate that IFN-α enhances the B cell responses induced by SA + IL-2 through direct interactions between monocytes and B cells that do not involve lymphocyte-function-associated-I molecules, intercellular adhesion molecule-I, or HLA-DR antigens. Thus, the data demonstrate the presence of unique direct interactions between B cells and monocytes that regulate human B cell responsiveness.