Type IV collagen α‐chain composition in synovial lining from trauma patients and patients with rheumatoid arthritis

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Abstract
Objective Normal synovial lining is composed of macrophage‐like type A and fibroblast‐like type B lining cells. This sheet‐like structure lacks a basement membrane, but its intercellular substance contains some basement membrane components, including type IV collagen. We undertook this study to determine the α‐chain composition of type IV collagen in normal and arthritic synovial lining, using monoclonal α‐chain antibodies. Methods Samples were analyzed using avidin–biotin–peroxidase complex staining for the presence of collagen α1/2(IV), α3(IV), α4(IV), α5(IV), α6(IV), matrix metalloproteinase 2 (MMP‐2), and MMP‐9, and the enzyme activity was detected using gelatin zymography. Double immunofluorescence was performed for type IV collagen/MMP‐9 and type IV collagen/CD68. Synovial fibroblasts were studied using quantitative reverse transcriptase–polymerase chain reaction. Results In mildly inflamed synovium from 5 trauma patients, α1/2(IV) chains were strongly stained, but α5(IV) and α6(IV) chains were weakly stained. Coding messenger RNA was shown in cultured synovial fibroblasts. Basement membranes of blood vessels contained all α(IV) chains and served as useful positive sample controls. In the synovial lining from 5 patients with rheumatoid arthritis (RA), all α‐chains were absent/very weakly stained. This was coupled with numerous type A lining cells containing MMP‐9 (type IV collagenase), also found in synovial fluid. Conclusion Synovial lining has a unique and very limited α‐chain composition, different from that of the vascular basement membrane, which contains all α‐chains. This special composition and lack of nidogen are probably of relevance for the bidirectional translining diffusion. Such tentative α‐chain–dependent adhesive and transport‐regulating properties seem to be deranged in RA, probably in part due to type IV collagenases produced in the lining and/or released by transmigrating or synovial fluid neutrophils.