Differential expression of integrin subunits in canine knee ligament fibroblasts

A method for measuring the expression of integrin subunits on the cell surf ace of knee ligament fibroblasts was developed with use of flow cytometry a nd immunofluorescence. The ligament cells exhibited uniform size and densit y, as shown by forward and side-scatter properties, and showed minimal nons pecific binding of isotype control antibodies compared with unstained cells . All cells expressed the alpha 5 integrin subunit; lateral collateral liga ment cells stained with antibody to alpha 5 showed a mean fluorescence inte nsity 2-fold higher than that of medial collateral ligament cells, 1.5-fold higher than that of posterior cruciate ligament cells, and 3-fold higher t han that of anterior cruciate ligament cells, indicating a greater expressi on of the alpha 5 subunit by lateral collateral ligament cells than by medi al collateral, posterior cruciate, and anterior cruciate ligament cells. Al l cells expressed the pi integrin subunit; the expression by posterior cruc iate ligament cells was 3-fold higher than that by medial collateral ligame nt or lateral collateral ligament cells and 5-fold higher than that by ante rior cruciate ligament cells. All cells expressed the beta 3 integrin subun it; the expression by posterior cruciate ligament cells was 1.5, 3, and 4.5 -fold greater than that by lateral collateral, anterior cruciate, and media l collateral ligament cells, respectively. Our data suggest there is a diff erential expression of integrin subunits in knee ligament fibroblasts, and this in part may explain differences in their attachment and adherence to e xtracellular matrix molecules.