INTEGRIN DISPLAY INCREASES IN THE WOUNDED RABBIT MEDIAL COLLATERAL LIGAMENT BUT NOT THE WOUNDED ANTERIOR CRUCIATE LIGAMENT

The differential capacities of the anterior cruciate and medial collat eral ligaments to heal may be related to differences in cellular funct ion. This study tested the hypothesis that differential expression of integrins occurs in these Ligaments after injury. The integrins are a family of cell surface receptors that mediate adhesion, migration, and other cellular functions critical to the healing of a wound. A simila r complement and amount of the beta(1) subfamily of integrins are know n to be present on the unperturbed anterior cruciate and medial collat eral ligaments in humans and rabbits. A partial laceration was surgica lly created in these two ligaments in 12 anesthetized New Zealand Whit e rabbits. Immunohistochemistry was performed on sections from the lig aments at 1, 3, 7, and 10 days after injury, using monoclonal antibodi es directed against the integrin subunits beta(1), alpha(5), alpha(6), and alpha(v). Between 3 and 7 days, the wounded medial collateral lig ament demonstrated a striking increase in staining for the beta(1), al pha(5), and alpha(v) subunits on the fibroblasts, within the repair si te, and on capillary endothelium. Increased staining was most marked f or the beta(1) subunit and less marked for the alpha(5) and alpha(v) s ubunits. The alpha(6) subunit stained exclusively vascular structures within the healing medial collateral ligament. In marked contrast, the anterior cruciate ligament, which does not mount an effective repair response, demonstrated no comparable alteration of integrin expression from baseline levels. This study demonstrates that increased expressi on of integrins occurs coincident with wound healing in the medial col lateral ligament, whereas this expression remains at baseline levels i n the nonhealing wounded anterior cruciate ligament. This observation suggests that a failure to alter expression of integrins subsequent to injury may play a role in the defective healing of the anterior cruci ate ligament.