Artificial exudate: stimulation of cell proliferation by plasma not serum is associated with fibrinolysis

Despite its abundance of cell culture growth factors, serum does not enhance growth of the in vivo test system, the chick chorioallantoic membrane (CAM). Previously we have also shown that fibrinogen (Kabi) and its degradation products do not display mitogenic activity on the CAM, but have now been surprised to find stimulation of DNA synthesis (up to 2.5-fold) 18 h after application of human plasma [incorporation of [3H]thymidine control mean +/- SEM 8442 +/- 1338 dpm/CAM (n = 8); test--20 199 = 3491 (n = 6); t-test P less than 0.01)]. Plasma (platelet-rich and platelet-poor) was freshly prepared by minicolumn removal of citrate at 16 degrees C; 0.3 ml aliquots of 10% human plasma were applied to the CAM and groups were fixed at various time intervals. Cross-sections were examined histologically, including immunoperoxidase studies with antihuman fibrinogen which does not cross react with chick fibrinogen, and autoradiography with [3H]thymidine. Initially, a layer of plasma was observed on the surface of the CAM. After 1 h a condensed fibrillar layer of fibrin was formed and was still present at 6 h. This was associated with increased [3H]thymidine labelling of the surface layer of the CAM. By 18 h the fibrin had disappeared, indicating that it had been lysed by the CAM, and widespread [3H]thymidine labelling was observed. No inflammatory cell infiltrate was apparent, but marked oedema developed. Oedema alone was observed in controls receiving serum or Dulbecco buffer. Both platelet-rich and platelet-free plasma gave stimulation of mitogenic activity, implying that platelet-derived growth factor is not involved in the stimulation of the CAM.(ABSTRACT TRUNCATED AT 250 WORDS)