CHONDROCYTE HETEROGENEITY - IMMUNOHISTOLOGICALLY DEFINED VARIATION OFINTEGRIN EXPRESSION AT DIFFERENT SITES IN HUMAN FETAL KNEES

During development and at maturity different forms of cartilage vary i n morphology and macromolecular content, This reflects heterogeneity o f chondrocyte activity, in part involving differential interactions wi th the adjacent extracellular matrix via specialized cell surface rece ptors such as integrins. We undertook an immunohistological study on a series of human fetal knee joints to assess variation in the expressi on of integrins by chondrocytes and potential matrix ligands in articu lar, epiphyseal, growth plate, and meniscal cartilage. The results sho w that articular chondrocytes (beta 1+, beta 5 alpha V+, alpha 1+, alp ha 2+/-, alpha 5+, weakly alpha 6+, alpha V+) differed from epiphyseal (beta 1+, beta 5 alpha V+, alpha 1+/-, alpha 2+/-, alpha 5+, alpha 6, alpha V+) growth plate (beta 1+, beta 5 alpha V+, alpha 1-, alpha 2- , alpha 5+, alpha 6+, alpha V+), and meniscal cells (beta 1+, beta 5 a lpha V+, alpha 1+, strongly alpha 2+, alpha 5+, alpha 6+, alpha V+ in expression of integrin subunits, There was no expression of beta 3, be ta 4, beta 6, or alpha 3 by chondrocytes. These results differ from pr evious reports on the expression of integrins by adult articular carti lage, where alpha 2 and alpha 6 are not seen. Variation in distributio n of matrix ligands was also seen, Fibronectin, laminin and Type VI co llagen were expressed in all cartilages but there was restricted expre ssion of tenascin, ED-A and ED-B fibronectin isoforms (articular carti lage and meniscus), and vitronectin (absent from growth plate cartilag e). Regulated expression of integrins by chondrocytes, associated with changes in the pericellular matrix composition, is of potential impor tance in control of cartilage differentiation and function in health a nd disease.