Preparation of soluble immune response suppressor and macrophage-derived suppressor factor

Abstract

Concanavalin A-activated murine suppressor T cells act via the mediator, soluble immune response suppressor (SIRS) which non-specifically suppresses IgM and IgG antibody responses to a variety of antigens, cytotoxic T lymphocyte responses and proliferative responses to alloantigens and mitogens in vitro. SIRS is a protein with an apparent MW of 45,000–55,000; the target of SIRS is the macrophage (Mø). Mø following treatment with SIRS release a second factor, Mø-derived suppressor factor (Mø-SF), which is directly responsible for the observed suppression of responses. Moreover, Mø-SF appears to be modified SIRS by all criteria used to date; Mø-SF can be obtained by reacting SIRS with low concentrations of H 2O 2 in the absence of Mø. Thus, Mø appear to serve only as a source of H 2O 2 and the mechanism of Mø-SF action appears to have an oxidative basis. Mø-SF activity is lost following treatment with sulfhydryl reagents such as 2-mercaptoethanol, dithiothreitol or cysteine, reducing agents such as NaBH 4 and a variety of peroxidase substrates such as pyrogallol, phenylenediamine, and ascorbic acid. Additionally, Mø-SF-mediated inhibition can be reversed by high concentrations of 2-mercaptoethanol or dithiothreitol under appropriate conditions. Since Mø-SF appears to be modified SIRS, oxidized by peroxide, and not a distinct second mediator produced by Mø in response to SIRS, we propose eliminating the term Mø-SF and using SIRS ox to denote the active form of SIRS produced either by the SIRS-H 2O 2 reaction or SIRS-treated Mø.