Adhesion molecule expression in human synovial tissue

We have previously shown that E-selectin is expressed on endothelium in rheumatoid arthritis (RA) synovial tissues, and hence may be important in recruitment of leukocytes into the inflamed joint. In the present study, we determined whether other cellular adhesion molecules, including selectins and members of the integrin and immunoglobulin supergene families, are expressed in frozen synovium.

We employed immunohistochemical staining to determine the distribution of CD31 (PECAM), CD44 (hyaluronate receptor), CD62 (P-selectin), Leu-8 (L-selectin), and the integrin subunits alpha 5 (VLA-5), alpha 6 (VLA-6), beta 1 (VLA 1-6), and beta 3 (vitro-nectin receptor), in synovial tissue from 9 RA and 9 osteoarthritis (OA) patients, and from 3 normal (NL) subjects.

P-selectin was expressed on vascular endothelium in all synovial tissues examined. L-selectin and alpha 5-integrin, while expressed on a variety of cell types, were not differentially expressed on RA synovial tissues. Integrin subunits alpha 6 and beta 1 were down-regulated on some RA synovial tissue components. In contrast, CD31 was expressed to a greater extent on RA than on OA lining cells and macrophages (P < 0.05). CD44 was expressed to a greater extent on RA or OA macrophages, lining cells, and fibroblasts compared with NL (P < 0.05). Integrin subunit beta 3 was strongly expressed on RA synovial blood vessels compared with NL (P < 0.05).

The expression of integrins VLA 1-6, and selectins P and L is not up-regulated in RA synovial tissues. CD31 and CD44 are up-regulated on RA macrophages and lining cells, CD44 on RA fibroblasts, and beta 3-integrin on RA blood vessels. The up-regulation of CD31, CD44, and beta 3-integrin in RA synovial tissues may help tip the balance of adhesive interactions toward passage and retention of leukocytes in the inflamed joint.