Molecular mass analysis of murine immunosuppressive immunoglobulin G-binding factors (IgG-BFs) produced by T-cell hybrids

Abstract

Induced and constitutive murine IgG-binding factors (IgG-BFs) have been purified by affinity chromatography from supernatants of T-cells preincubated with or without murine monoclonal IgG1 and IgG2b, respectively. IgG-BF M r values have been studied by SDS-polyacrylamide gel electrophoresis (PAGE) after treatment with SDS under conditions which do not noticeably alter their immunosuppressive activities on the secondary in vitro IgG antibody response. Suppression was recovered at M r values of 80000, 40000 and 20000. When induced IgG-BF was tested, the isotype-specific suppressive activity was found only at 40 kDa. The 20-kDa moiety appeared to derive from the 40-kDa component and the material found at 80 kDa exerted non-specific immunosuppressive effects. We conclude therefore that isotype-specific IgG-BF has an apparent M r of 40000.