SOLUBLE FCR BLOCK SUPPRESSOR T-CELL ACTIVITY AT LOW CONCENTRATION IN-VITRO ALLOWING ISOTYPE-SPECIFIC ANTIBODY-PRODUCTION

IgA and IgG binding factors (BF) can be found in the supernatant (T-h SUP) Of cultures containing macrophages and CD4(+) T cells stimulated with particulate antigens such as SRBC. Previous work indicated that t hese IgBF, when mixed with normal serum immunoglobulin, could block th e activity of suppressor T cells (T-s) and allow IgA and IgG PFC respo nses in vibro. We present serologic and functional evidence that IgABF and IgGBF in T-h sup are soluble Fc alpha R and Fc gamma RII(or III), respectively. Th sup adsorbed on affinity columns containing anti-Fc gamma RII/III mAb or murine IgG failed to augment IgG PFC responses. M aterial eluted from either the IgG or anti-Fc gamma RII/ III columns c ould be added back, interchangeably, to the adsorbed T-h sup and resto re IgG PFC. Recombinant murine Fc gamma RII (rFc gamma RII), added to the same adsorbed T-h sup at 0.01 to 0.5 ng/ml, resulted in a similar augmentation of IgG PFC. Interestingly, much higher concentrations of rFc gamma RII (10-100 ng/ ml) could not, augment IgG; PPC responses. P rotein dot blots showed that T-h sup and the eluted material from muri ne IgG: columns contained structures reactive with the Fc gamma RII/II I mAb. Similar studies using purified Fc alpha R revealed that IgABF e luted from IgA or anti-Fc alpha R columns was in fact Fc alpha R. Cros s-adsorption studies indicated clearly that the IgGBF (Fc gamma RII/II I) and the IgABF (FC alpha R) were separate molecules produced in the same T-h sup and that each regulated their respective Ig isotype indep endently. Thus, cultures of splenic macrophage and CD4(+) T cells, in the presence of particulate antigens such as SRBC, generate both Fc ga mma RII/III and Fc alpha R. This soluble FcR in combination with serum Ig act to block isotype-specific T-s cells at low concentration in vi tro. (C) 1996 Academic Press, Inc.