Platelet-derived growth factor and transforming growth factor-beta enhance tissue repair activities by unique mechanisms.

Platelet-derived growth factor (PDGF) and transforming growth factor-beta (TGF-beta) markedly potentiate tissue repair in vivo. In the present experiments, both in vitro and in vivo responses to PDGF and TGF-beta were tested to identify mechanisms whereby these growth factors might each enhance the wound-healing response. Recombinant human PDGF B-chain homodimers (PDGF-BB) and TGF-beta 1 had identical dose-response curves in chemotactic assays with monocytes and fibroblasts as the natural proteins from platelets. Single applications of PDGF-BB (2 micrograms, 80 pmol) and TGF-beta 1 (20 micrograms, 600 pmol) were next applied to linear incisions in rats and each enhanced the strength required to disrupt the wounds at 5 d up to 212% of paired control wounds. Histological analysis of treated wounds demonstrated an in vivo chemotactic response of macrophages and fibroblasts to both PDGF-BB and to TGF-beta 1 but the response to TGF-beta 1 was significantly less than that observed with PDGF-BB. Marked increases of procollagen type I were observed by immunohistochemical staining in fibroblasts in treated wounds during the first week. The augmented breaking strength of TGF-beta 1 was not observed 2 and 3 wk after wounding. However, the positive influence of PDGF-BB on wound breaking strength persisted through the 7 wk of testing. Furthermore, PDGF-BB-treated wounds had persistently increased numbers of fibroblasts and granulation tissue through day 21, whereas the enhanced cellular influx in TGF-beta 1-treated wounds was not detectable beyond day 7. Wound macrophages and fibroblasts from PDGF-BB-treated wounds contained sharply increased levels of immunohistochemically detectable intracellular TGF-beta. Furthermore, PDGF-BB in vitro induced a marked, time-dependent stimulation of TGF-beta mRNA levels in cultured normal rat kidney fibroblasts. The results suggest that TGF-beta transiently attracts fibroblasts into the wound and may stimulate collagen synthesis directly. In contrast, PDGF is a more potent chemoattractant for wound macrophages and fibroblasts and may stimulate these cells to express endogenous growth factors, including TGF-beta, which, in turn, directly stimulate new collagen synthesis and sustained enhancement of wound healing over a more prolonged period of time.

Transforming growth factor beta reverses the glucocorticoid-induced wound-healing deficit in rats: possible regulation in macrophages by platelet-derived growth factor.

Transforming growth factor beta (TGF-beta) and the platelet-derived growth factor (PDGF) are potent mitogenic polypeptides which enhance rates of wound healing in experimental animals; in contrast, glucocorticoids inhibit wound repair. The potential of TGF-beta and PDGF to reverse this inhibition in healing was tested in methylprednisolone-treated rats with deficits in skin wound strength of 50%. Single applications of TGF-beta (10-40 pmol per wound, 0.25-1 micrograms) applied locally at the time of wounding fully reversed this deficit in a concentration-dependent and highly reproducible manner. Wounds in glucocorticoid-treated animals were characterized by a near total absence of neutrophils and macrophages and by a delayed influx and reduced density of fibroblasts; however, such wounds treated with TGF-beta showed significant increases in wound fibroblasts and in intracellular procollagen type I. PDGF did not reverse the deficit in wound breaking strength in glucocorticoid-treated rats; there were more fibroblasts in the PDGF-treated wounds, but these fibroblasts lacked the enhanced expression of procollagen type I found in TGF-beta-treated wounds. The wound macrophages, required for normal tissue repair, remained absent from both PDGF- and TGF-beta-treated wounds in glucocorticoid-treated animals. This result suggested that macrophages might normally act as an intermediate in the induction of procollagen synthesis in fibroblasts of PDGF-treated wounds and that TGF-beta might bypass the macrophage through its capacity to stimulate directly new synthesis of procollagen type I in fibroblasts. Whereas PDGF does not stimulate procollagen synthesis, in a rodent macrophage cell line, PDGF induced a highly significant, time-dependent enhancement of expression of TGF-beta.

Idiotypes of anti-Ia antibodies. II. Effects of in vivo treatment with xenogeneic anti-idiotype.

The effects of in vivo treatment with xenogeneic anti-idiotypic antibodies were examined in an anti-Ia idiotypic system. Monoclonal antibody 14-4-4S, specific for Ia.7, has been shown to bear idiotopes that are expressed at readily detectable levels in conventional alloantibody responses. Sera from mice treated with purified anti-idiotypic antibodies (anti-Id) were found to contain inhibitory activity in an ELISA specific for the 14-4-4S Id, whereas sera from control mice treated with heterologous normal Ig did not. In addition, sera of anti-Id-treated C3H.SW mice contained specific anti-I-E activity, shown by binding to B10.A(2R) but not B10.A(4R) LPS blasts in flow microfluorometry. The anti-I-E induced by anti-Id included more IgG1 than IgG2. Even though a significant amount of anti-I-E activity was present in the serum, absorption analysis showed that most of the idiotope-positive antibody was not I-Ek-specific. Penetrance of induction of anti-I-E by anti-Id was 100% in the C3H.SW mice tested, and activity persisted in the serum for at least 8 to 9 mo in some cases. B10 mice produced only marginal anti-I-E activity after treatment, suggesting that induction is due to specific triggering rather than due entirely to a resemblance of anti-Id to the I-E antigen. The results thus indicate long-lasting alterations in an anti-Ia idiotypic system in the absence of exposure to conventional antigen, and represent specific manipulation of anti-Ia immunity.

Mechanisms of immune lysis. I. Physiological distinction between target cell death mediated by cytotoxic T lymphocytes and antibody plus complement.

The pattern of progressive release of cytosolic (52Cr) and nuclear (125IUdR) labels from normal or tumor cells being lysed by CTL is strikingly different from the pattern observed when similar cells are lysed by Ab + C or hypotonic shock. We propose that these differences reflect physiologic differences in the lytic events associated with Ab + C- and CTL-mediated cell death.