EXPRESSION OF INTEGRIN FAMILY OF CELL-ADHESION RECEPTORS IN RHEUMATOID SYNOVIUM - ALPHA-6 INTEGRIN SUBUNIT IN NORMAL AND HYPERPLASTIC SYNOVIAL LINING CELL LAYER

Integrins are heterodimeric cell adhesion receptors. The beta1 integri n subunit can be in a complex with multiple a subunits and form recept ors for collagen, laminin, fibronectin and vitronectin. We have charac terized the distribution of eight integrin subunits in rheumatoid syno vium, with special interest in the lining cell layer. The beta1 integr in subunit was found in abundance in synovial stroma and in lining cel ls. The only alpha subunit seen constantly in lining cells was alpha6. In complex with a beta subunit, alpha6 forms a laminin receptor usual ly seen in epithelial or endothelial cells or in macrophages. The fact that laminin was found in the extracellular matrix around synovial ce lls suggests the importance of alpha6 integrin in the adhesion of syno vial lining cells. Furthermore, alpha6 expression was noticeably weake r in strongly proliferative lining cell layers, indicating that the in flammatory process may regulate integrin expression. A potential conne ction between altered expression of cell adhesion receptors and the pa thological behavior of rheumatoid lining cells is suggested.