IMMUNOMODULATING PROPERTIES OF PRODIGIOSIN 25-C, AN ANTIBIOTIC WHICH PREFERENTIALLY SUPPRESSES INDUCTION OF CYTOTOXIC T-CELLS

An antibiotic, prodigiosin 25-C, preferentially suppresses cytotoxic T lymphocytes (CTL) without affecting antibody production. Here, we investigated the effect of prodigiosin 25-C on delayed-type hypersensitivity (DTH), graft versus host reaction (GvHR) and allogeneic skin graft rejection. DTH reactions were markedly inhibited by ip treatment of the mice with prodigiosin 25-C. Cell transfer experiments indicated that prodigiosin 25-C exerted its suppressive effect on the late efferent phase rather than on the induction phase of DTH. Prodigiosin 25-C suppressed induction of anti-host CTL when GvHR was induced by iv inoculating splenocytes of parental C57BL/6 mice to adult unirradiated BDF1 mice. It had little effect on GvHR-induced splenomegaly observed 2 weeks after the inoculation, but significantly delayed the subsidence of splenomegaly as revealed 8 weeks later, suggesting that suppression of CTL converts immunosuppressive GvHR to immunostimulative one as reported by G. M. SHEARER. However, reduction of interleukin-2 (IL-2) production and mitogen responses induced by GvHR were not rescued by prodigiosin 25-C treatment. Prodigiosin 25-C moderately prolonged survival of major histocompatibility (MHC)-mismatched skin grafts. Since the mode of action of prodigiosin 25-C is distinct from those of cyclosporin A and FK506, these results demonstrate potential usefulness of the antibiotic for a supplementary immunosuppressant.