INCORPORATION OF THYMIDINE BY FIBROBLASTS - EVIDENCE FOR COMPLEX REGULATION BY POSTSURGICAL MACROPHAGES

Macrophages and fibroblasts are major components of the postsurgical repair process. In order to understand more fully the interaction between these two cell types, we studied the modulation by macrophages of the incorporation of [3H]thymidine into postsurgical fibroblasts recovered from the site of peritoneal injury. Peritoneal exudate cells (PEC): (> 95% macrophages) were collected from rabbits 4 and 7 days after resection and reanastomosis of the small intestine. PEC were suspended in Medium 199 (M-199) with 3% fetal calf serum (FCS) and incubated for 48 hr. Fibroblasts were obtained from rabbits that underwent abrasion of the parietal peritoneum 7 days previously, and were cultured for 7 days in M-199 with 3% FCS. Fibroblasts were then repeated and incubated with macrophage-spent medium. Incorporation of [3H]thymidine into fibroblasts was significantly suppressed after 24 hr of incubation with macrophage-spent media compared to the incorporation by fibroblasts incubated with fresh medium (control). This suppression was most profound when fibroblasts were incubated with resident (nonsurgical) macrophage-spent medium. The incorporation of thymidine by macrophage-spent media groups then increased rapidly and reached control levels at 48 hr of incubation. After 54 hr of incubation, the incorporation of thymidine by fibroblasts incubated with media from postsurgical macrophages was significantly higher than that of control. Morphological changes in fibroblasts also appeared as the culture with macrophage-spent media progressed. Initially, fibroblasts were shaped like pine needles, but after 7 days of culture, fibroblasts assumed a spherical shape. Round-shaped fibroblasts returned to the original morphology (pine needle shape) after incubation for 48 hr with macrophage-spent medium. These data suggest that the supernatant obtained from cultures of peritoneal macrophages contains material(s) which initially suppresses the proliferation of fibroblasts and then activates them after a lag period. This modulation of proliferation is temporally associated with morphological transformation.