Immunofluorescence Analysis of NF-kB and iNOS Expression in Different Cell Populations during Early and Advanced Knee Osteoarthritis

Synovitis of the knee synovium is proven to be a precursor of knee osteoarthritis (OA), leading to a radiologically advanced stage of the disease. This study was conducted to elucidate the expression pattern of different inflammatory factors—NF-kB, iNOS, and MMP-9 in a subpopulation of synovial cells. Thirty synovial membrane intra-operative biopsies of patients (ten controls, ten with early OA, and ten with advanced OA, according to the Kellgren–Lawrence radiological score) were immunohistochemically stained for NF-kB, iNOS, and MMP9, and for different cell markers for macrophages, fibroblasts, leukocytes, lymphocytes, blood vessel endothelial cells, and blood vessel smooth muscle cells. The total number of CD68+/NF-kB+ cells/mm2 in the intima of early OA patients (median = 2359) was significantly higher compared to the total number of vimentin+/Nf-kB+ cells/mm2 (median = 1321) and LCA+/NF-kB+ cells/mm2 (median = 64) (p < 0.001 and p < 0.0001, respectively). The total number of LCA+/NF-kB+ cells/mm2 in the subintima of advanced OA patients (median = 2123) was significantly higher compared to the total number of vimentin+/NF-kB+ cells/mm2 (median = 14) and CD68+/NF-kB+ cells/mm2 (median = 29) (p < 0.0001). The total number of CD68+/iNOS+ cells/mm2 in the intima of both early and advanced OA patients was significantly higher compared to the total number of vimentin+/iNOS+ cells/mm2 and LCA+/iNOS+ cells/mm2 (p < 0.0001 and p < 0.001, respectively). The total number of CD68+/MMP-9+ cells/mm2 in the intima of both early and advanced OA patients was significantly higher compared to the total number of vimentin+/MMP-9+ cells/mm2 and CD5+/MMP-9+ cells/mm2 (p < 0.0001). Macrophages may have a leading role in OA progression through the NF-kB production of inflammatory factors (iNOS and MMP-9) in the intima, except in advanced OA, where leukocytes could have a dominant role through NF-kB production in subintima. The blocking of macrophageal and leukocyte NF-kB expression is a possible therapeutic target as a disease modifying drug.