Temporal and spatial expression of transforming growth factor-β in the healing patellar ligament of the rat

We investigated the temporal and spatial expression of transforming growth factor‐β in the healing patellar ligament of the rat by immunohistochemistry. The mid‐portion of the medial half of the patellar ligament in 14‐week‐old male Wistar rats was cut transversely with a scalpel. On day 1 after ligament injury, diffuse staining for transforming growth factor‐β was observed in the extracellular matrix filling the wound, and the staining in the adjacent ligament tissue was as weak as it was in the normal ligament. On day 3, the intensity of the diffuse extracellular staining decreased, and the staining was observed in correspondence with the cellular distribution in the wound site and in the adjacent uninjured ligament tissue. On day 7, the intense staining was widely distributed over the whole length of the ligament tissue. On day 28, the staining for transforming growth factor‐β was still observed at the wound site and in the adjacent uninjured ligament tissue, where the staining was reduced in intensity but still stronger than it was in the normal ligament. On day 56, the expression of transforming growth factor‐β was still detectable at the wound site: however, in the adjacent uninjured ligament tissue, it had almost subsided to the normal level. The results of the present study suggest that ligament healing may be accompanied by extensive changes in the expression of transforming growth factor‐β over the whole length of ligament tissue.