Characterization of murine pregnancy decidua transforming growth factor beta. I. Transforming growth factor beta 2-like molecules of unusual molecular size released in bioactive form

A novel type of bioactive transforming growth factor beta 2 (TGF beta 2)-related immunosuppressive activity, lower in molecular mass (20-23 kDa) than a conventional TGF beta 2 standard (25 kDa), has been shown to be released by non-T non-B suppressor cells of murine decidua into fetal bovine serum (FBS)-containing tissue culture medium during a 48-h incubation at 37 degrees C. Substitution of a serum-free medium has allowed direct PAGE-Western blotting and the demonstration in supernatant (prior to incubation at 37 degrees C) of a TGF beta 2-immunoreactive doublet at a higher molecular mass (26 and 27 kDa) than the standard but with apparent immunosuppressive activity. When decidua were incubated in serum-free medium at 37 degrees C, immunosuppressive activity in the supernatant increased to peak at 18 h in association with the appearance of the previously described lower molecular mass species of molecule. The doublet did not appear to be the result of glycosylation of a conventional 25-kDa TGF beta 2 and could be converted into the lower molecular mass form by incubation for 18 h at 37 degrees C, with pH 4.5 but not with pH 7.5 buffer; this incubation in the absence of decidual cells was not accompanied by increased immunosuppressive activity. This transformation could be blocked by a brief heating of the supernatant to 80 degrees C for 10 min to destroy enzymes present in supernatant prior to mixing with the acidic buffer, but biologic activity neutralizable by anti-TGF beta 2 was retained.