ISOLATION AND PARTIAL CHARACTERIZATION OF MESSENGER RNA, FROM BINDING FACTOR' MURINE T CELL HYBRIDS, CODING FOR SUPPRESSIVE IMMUNOGLOBULIN G
Résumé
From the 'Unite INSERM U 196 and 'Unite INSERM U 255. Institut Curie, 26, rue d'Ulm. 75005-Paris Poly A RNA has been isolated from a murine T cell hybridoma (TzD4) that spontaneously secretes suppressive immunoglobulin G-binding factor (IgGBF). Translation products, obtained from a rabbit reticulocyte lysate translation system and after injection into Xenopus Zaeuis oocytes, contain material with the biologic activity, the affinity, and the m.w. of murine IgGBF; it suppresses secondary in vitro IgG antibody production in a dose-dependent fashion. The suppressive factor binds to IgG but not to IgM immunoadsorbents and, after mild NaDodSO, treatment, dissociates in NaDodSO, polyacrylamide gels into two peaks at 78 and 40 kD. Translation products from two non-IgGBF-secreting cell lines (BW-5147, a T lymphoma line, and Ae, a fibroblast cell line) fail to exert any suppressive activity. On sucrose gradients, the RNA responsible for the bio-logic activity was found in one major peak located at 11s. IgGBF synthesized in a cellfree translation system by using poly A RNA and sucrose gradient fractions was also characterized by immunoprecip-itation with Fc fragments of [35S]methionine-labeled proteins. On NaDodSO, polyacrylamide gels, it migrates in one peak located at 37 kD. We conclude that IgGBF is coded for by 11s poly A RNA and that no post-translational modifications (other than pro-teolytic cleavage) are necessary to obtain a biologically active factor with Ig-binding properties. The production of Ig classes and subclasses by B cells is regulated by T cell factors (l) , among which immuno-globulin-binding factors (IBF)3 may play a major role (2). Produced by Fc receptor (FcR)-positive T cells, these factors bind specifically to the Fc portion of Ig and modulate the in vitro production of the corresponding Ig isotype. Three different isotype-specific T cell factors have been
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