Synovitis in osteoarthritic patients: Morphological and virological evidence of its contribution to development of the disease

The role of inflammation in the development of osteoarthritic joint degeneration is not completely understood. Recent data suggest that processes that cause and orchestrate inflamed synovial lesions may be implicated in the development of the disease. The morphological changes of the synovium in patients with osteoarthritis (OA), as well as the level of synovial inflammation cautiously graded, in association to the presence of human parvovirus B19 (B19V) infection markers, were evaluated. Qualitative and quantitative detection of B19V genomic sequence was performed in OA and rheumatoid arthritis (RA) groups. The expression of CD68, S100 (Ca²⁺ binding proteins soluble in 100% ammonium sulfate) and B19 VP1/VP2 capsid proteins found in the synovium were investigated by single and double immunolabeling, whereas fine features of synoviocytes - by electron microscopy. One-third of OA and RA patients demonstrated synovial expression of B19V antigen, which was confirmed in both types of synoviocytes. The overall expression of B19V in OA patients was weaker than that found in RA subjects. Positive correlation between B19V-positive vascular endothelial cells, sublining infiltrating lymphocytes, macrophages, and B19V-positive synoviocytes was established. No correlation between synovitis score indices as well as the expression of S100 and expression of B19V was found. The results suggest that the synovial membrane maintains local joint homeostasis, and that virus mediated synovitis is implicated in the development of OA.