CHARACTERIZATION OF MURINE PREGNANCY DECIDUA TRANSFORMING GROWTH-FACTOR-BETA .1. 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 doubler did not appear to be the result of glycosylation of a conventional 25-kDa TGF beta 2 and could be convened 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. These data suggest that TGF beta 2-like immunoregulatory activity in murine decidua is biologically active and that the size of the molecules may be modified by local enzymatic activity. The immunosuppressive factor was shown to be capable of stimulating procollagen production by confluent human fibroblasts assayed by HPLC measurement of hydroxyproline; but, in comparison to an authentic TGF beta 2 standard, the potency was much lower. On this basis, it would be possible to have local active immunosuppression without stimulation of fibrosis in implantation site decidua.