Studies on thermophile products. V. Immunosuppressive profile in vitro of Bacillus stearothermophilus component, Fr.5-B.

The immunosuppressive profile of Bacillus stearothermophilus UK563 component, Fr.5-B, is presented in in vitro studies. Fr.5-B (0.1-1000 ng/ml), provided it was added at the initiation of mixed leukocyte reaction (MLR), inhibited dose-dependently the incorporation of tritiated thymidine (3H]TdR) into mouse spleen cells and human peripheral blood lymphocytes. Even the addition of Fr.5-B 48 h after the onset of culture suppressed mouse MLR, unlike cyclosporin A (CYA). Fr.5-B significantly inhibited cytotoxic T lymphocyte generation determined by 3H]TdR-release micro-cytotoxicity assay by using mouse mastocytoma P815 as targets. Moreover, this component decreased dose-dependently the expression of class II major histocompatibility molecules (Ia) on mouse peritoneal macrophages induced by concanavalin A supernatant. The present results revealed the unique immunosuppressive property of Fr.5-B which was different from that of CYA.