Characterization of T-cell-soluble factors modulating the expression of Ia and H-2 antigens on BALB/c B lymphoma cell lines

The effect of supernatants of concanavalin A-activated spleen cells (CAS) on the expression of various antigens, especially Ia antigens, on BALB/c B lymphoid cells, was examined. This study demonstrates the following: (i) CAS enhanced the expression of Ia antigens on four out of five BALB/c lymphoid cell lines. (ii) CAS selectively modulates the expression of Ia and H-2D, but not sIgM or viral gp70 expression, on X16C 8.5 tumor cells. The enhanced levels of Ia expression on B lymphoid tumor cells were also detected by using anti-Ia monoclonal antibodies. (iii) The molecular weight of soluble factor(s) affecting Ia and H-2 was approximately 40,000 estimated by gel filtration on a Sephadex G-200 column. (iv) Type 1 interferon but not interleukin 1, interleukin 2, or T-cell-replacing factor enhanced the expressions of Ia and H-2D antigens. (v) The activity of CAS-modulating Ia and H-2 antigens was eliminated by acidic treatment. It was concluded from this study that at least one of the factor(s) in CAS, modulating the antigenic expression of B-lymphoid cells, was interferon-like in nature. From our findings, a possible immunoregulatory mechanism by interferon was suggested: T cells, after stimulation of mitogens or antigens, secrete interferons which modulate the expression of Ia and H-2 on B cells. Then B cells, whose Ia and H-2 were modulated selectively by T-soluble factors(s), might interact with T cells much more efficiently.