LOCALIZATION OF THE ALPHA-V SUBFAMILY OF INTEGRINS AND THEIR PUTATIVELIGANDS IN SYNOVIAL LINING CELL LAYER

Objective. The lining cell layer of the synovium proliferates strongly in rheumatoid arthritis. It has been suggested that it has a central role in the destruction of cartilage. We have analyzed the structure o f the extracellular matrix and the adhesion molecules of normal, osteo arthritic and rheumatoid lining cell layer. Methods. We localized the av integrin subunit and its 4 putative partner beta subunits in synovi al samples by using indirect immunofluorescence. The specimens were al so analyzed by confocal microscopy. Indirect immunofluorescence was al so used to analyze the ligands of av integrins, namely fibronectin and vitronectin. Results. The alpha v integrin was abundant in the lining cell layer of normal and osteoarthritic synovia, whereas it was not e xpressed in the proliferating rheumatoid lining cell layers. A similar expression pattern was found for beta 5 subunit, suggesting that it i s the major partner for cuv. However, also some alpha v beta 1 and alp ha v beta 3 heterodimers may be present. The confocal microscopy revea led the presence of both alpha v beta 5 positive and negative lining c ells. The putative ligands for alpha v integrins, namely fibronectin a nd vitronectin were found in the lining cell layer of all the synovial specimens. Conclusion. In spite of the proliferation of the lining ce ll layer in rheumatoid inflammation, the extracellular matrix stays ve ry similar to that in normal and osteoarthritic synovium, whereas the pattern of the adhesion receptors is completely altered.