Intrinsic properties of ACL and MCL cells and their responses to growth factors.

Different intrinsic properties of the constituent cells of the anterior cruciate ligament (ACL) and medial collateral ligament (MCL) have been proposed to be one of the factors in the differential repair mechanisms. We have found that the outgrowth of cells from rabbit ACL explants was slower than from MCL explants after 10 d. Growth curves of ACL and MCL cultures at both Passage numbers 2 and 6 showed a slower rate of proliferation of ACL cells than MCL cells (P < 0.005). The proliferative response of rabbit ACL and MCL cells to b-FGF and TGF-beta was also investigated. Both b-FGF and TGF-beta had no significant effect on cell proliferation of ACL and MCL cultures after 48 h. However, TGF-beta did have an inhibitory effect on thymidine incorporation, especially at concentrations greater than 1 ng.ml-1, while b-FGF stimulated thymidine incorporation in ACL and MCL in a dose-dependent manner. Differences in the cell morphology of the ACL and MCL cells grown in culture were seen also. Cells from Passages 3-6 demonstrated these differences more prominently, and phalloidin staining for actin showed that ACL cells appeared to have more intracellular actin fibers.