Effects of cyclosporin A on the immune system of the mouse. I. Evidence for a direct selective effect of cyclosporin A on B cells responding to anti‐immunoglobulin antibodies

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Abstract
Previous in vivo studies have shown that the immunsuppressive peptide cyclosporin A (CsA) selectively suppresses antibody responses to nonmitogenic T‐independent (TI‐2) antigens, but not those to mitogenic (TI‐1) antigens. This report demonstrates that in vitro CsA suppresses the polyclonal proliferative response of B cells to anti‐Ig (anti‐μ) antibodies at 300‐400‐fold lower doses than are required to inhibit B cell proliferation induced by lipopolysaccharide. Since the proliferative response to anti‐μ requires neither T cells nor macrophages, it is concluded that CsA has a direct inhibitory effect on the B cells responding to this mitogen. The data support the concept that the B cells responding to TI‐2 antigens are contained within the population which is stimulated polyclonally by anti‐μ, and that lipopolysaccharide stimulates a distinct B cell subpopulation. They do not, however, exclude the possibility that anti‐μ. and lipopolysaccharide stimulate the same B cell population via two biochemically distinct triggering mechanisms, one of which is CsA‐sensitive and the other CsA‐resistant.