LOWER CYTOKINE RELEASE BY FETAL PORCINE PLATELETS - A POSSIBLE EXPLANATION FOR REDUCED INFLAMMATION AFTER FETAL WOUNDING

Fetal dermal wound healing is unique because of its rapidity, minimal inflammation, and lack of scarring. Cytokines such as transforming gro wth factor beta (TGF-P) and platelet-derived growth factor (PDGF) evok e an inflammatory response and scarring when applied to fetal wounds. Because adult and fetal platelet counts are comparable, the aim of thi s study was to test the hypothesis that the minimal inflammatory respo nse seen in the fetus is attributable to differences in the serum cont ent of cytokines released by fetal platelets. Using Yorkshire swine, b lood was collected from 10 adults and 10 fetuses at day 60 of gestatio n (fullterm, 114 days). Platelets were isolated from anticoagulated bl ood and examined by transmission electron microscopy. Serum was analyz ed for PDGF-AB and TGF-beta 2 by enzyme-linked immunosorbent assay (EL ISA), and TGF-beta 1 by I-125 radioimmunoassay. TGF-beta samples were assayed with and without prior acid activation to determine the total TGF-beta and the biologically active form of the cytokine. Electron mi croscopy of adult and fetal platelets showed no gross structural diffe rences. Alpha granules, which contain cytokines as well as procoagulan t factors, were present in similar quantities and with the same degree of homogeneity. The cytokines analyzed were present in all the adult and fetal sera tested. However, PDGF-AB was present in significantly l ower concentrations in the fetus (383 +/- 72 pg/mL v 972 +/- 185 pg/mL in the adult; P <.05). In addition, the fetal samples contained lower amounts of TGF-beta 1 (13,895 +/- 1,770 v 29,864 +/- 5,050 pg/mL; P < .05) and TGF-beta 2 (6,758 +/- 734 v 13,407 +/- 1,395 pg/mL; P < .05) . The majority of TGF-beta was in latent form; the adult sera containe d significantly more active TGF-beta 1 and active TGF-beta 2 than the fetal sera. The ratios of active TGF-beta 1 to active TGF-beta 2 were similar for the adult (22.3) and fetus (18.5). However the ratio of to tal TGF-beta 1 to total TGF-beta 2 was significantly lower for the fet us (2.26 v 7.69). The authors conclude that although no gross differen ces in platelet ultrastructure were noted, fetal porcine platelets rel ease lower quantities of cytokines into serum. This lower serum cytoki ne content and the relative concentrations of TGF-beta 1 and TGF-beta 2 may explain, in part, the minimal inflammation and sparse fibrosis c haracteristic of fetal wounds. These observations provide further insi ght into the unique fetal response to wounding and may offer alternati ve avenues to modulate the postnatal wound healing response. Copyright (C) 1996 by W.B. Saunders Company