Expression of laminins and their integrin receptors in different conditions of synovial membrane and synovial membrane-like interface tissue

Objective-To demonstrate the expression of laminins (Lns) and their integrin (Int) receptors in different synovial samples and synovial membrane-like interface tissues from well fixed and aseptically loosened total hip replacement (THR), and the potential role of Ln-Int interaction in the production of collagenases and cytokines. Methods-Immunohistochemical staining was done to detect the distribution of EHS Ln, Ln alpha 2, alpha 3, alpha 5, beta 1, beta 2 chains and Int alpha 1, alpha 2, alpha 3, alpha 6, beta 1, beta 4 subunits in different samples. Double immunofluorescence labelling was used to find colocalisation of Int alpha 6 subunit and collagenase-1/collagenase-3/TNF alpha/IL6. Results-General Ln immunoreactivity was detected in all specimens. Ln alpha 5, beta 1 and beta 2, but not a2 and a3 chains were seen in the synovial lining and the basement membrane of blood vessels with the intensity/extent of labelling in the following rank order: rheumatoid arthritis (RA) loosened prostheses, osteoarthritis, well fixed prostheses, traumatic knees. Among Int subunits, staining for pr was usually the strongest, followed by staining for Int alpha 6, alpha 1, alpha 3, and alpha 2 subunits, with the same rank order for overall expression of Lns. Int beta 4 subunit was not detectable in most of the specimens. Double labelling focused on Int a6 subunit disclosed its frequent colocalisation with collagenases 1 and 3 and with tumour necrosis factor a and interleukin 6 in synovial lining. Conclusion-Synovial lining contains Ln-10, Ln-11, and Int alpha 6 beta 1 and alpha 1 beta 1 receptors. In aseptic loosening of THR, interface tissue has a similar Ln subtype and Int receptor composition as RA synovium, which confirms its "lining-like" phenotype. Synovial lining does not contain Ln-5 (alpha 3 beta 3 gamma 2) or Int alpha 6 beta 4, which are components of epithelial hemidesmosomes. The expression of Lns and their Int receptors is upregulated in inflammation. The close spatial relation between Ln and its Int receptors in synovial lining cells containing proteinases and cytokines suggests a potential role in joint destruction and prosthetic loosening.