INTERCELLULAR ADHESION MOLECULES IN NORMAL SYNOVIUM

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Abstract
The vasculature of normal synovium and skin has been examined for the presence of molecules believed to be involved in intercellular adhesion and whose expression on endothelial cells in vitro is known to be upregulated by cytokines Synovium was obtained from clinically and histologically normal joints removed during amputations for proximal sarcomata. Skin was obtained from healthy volunteers Cryostat sections of tissues were assessed by immunohistochemistry and microdensitometry for the presence of E-selectin using monoclonal antibody 1.2B6, intercellular adhesion molecule-1 (ICAM-1) using monoclonal antibody 6.5B5 and vascular cell adhesion molecule (VCAM-1) using monoclonal antibody 1.4C3. Both E-selectin and ICAM-1 were present on a proportion of normal synovial venules but at a level comparable to or lower than that found on dermal vessels. (Staining intensities given as mean absorption indices: superficial synovium 1.2B6: 9.9±11.4, 6.5B5: 10.2±12.0, deep synovium 1.2B6: 6.6±9.9, 6.5B5: 24.6±15.7, skin 1.2B6: 13.1±16.6, 6.5B5: 36.4±12.9.) E-selectin expression was most prominent on small superficial venules in synovium and ICAM-1 most strongly expressed on larger, deep venules. VCAM-1 was found at low levels on cells associated with vessel walls but no significant endothelial staining was seen in either type of tissue. VCAM-1 was also present on cells of the synovial lining layer. Some of the findings in synovium could have been attributable to tumour related cytokine release, but the consistency of findings and comparability to skin suggest that this is relatively unlikely. Baseline expression of endothelial adhesion molecules on vessels of different size and distribution may be important to the pattern of early cellular events which initiate chronic synovitis.

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