Objectives The initiation event in rheumatoid arthritis (RA) may be triggered by an infection and an association to various micro-organisms has been discussed. Micro-organisms capable of persistence, such as parvovirus B19 and Epstein-Barr virus, are of special interest. Features which might be expected of any micro-organism associated with RA, such as persistence, are also found in the protozoan Acanthamoeba polyphaga (AP). The aim of the present study was by means of immunohistochemical techniques, to search for epitopes in synovial tissue from RA patients and non-RA patients reacting/crossreacting with an AP specific monoclonal antibody.
Methods Patient material:Synovia and pannus was removed from the knee during arthroscopy or open joint surgery on 57 patients in a single surgical unit at Diakonhjemmet Hospital in Oslo. These patients were classified into three groups. One had a clinical diagnosis of RA (n = 30) according to the criteria of the American College of Rheumatology. The other 27 patients had degenerative joint disease (n = 17), or other inflammatory arthropathies (n = 10). The specimens were evaluated by light microscopy and immunohistochemistry. Monoclonal antibodies (MAb) against AP were produced by standard methods. A MAb reactive with the cytoplasm of AP and non-reactive with normal human skin biopsies was selected for use in immunohistochemistry.
Results Synovial membranes from RA patients demonstrated a distinct immunoreactivity whereas the reactivity in non-RA patients was weak. RA patients often demonstrated reactivity in the nuclear membrane in addition to cytoplasm and nucleus. The immunereactivity in non-RA patients was restricted to cytoplasm and nucleus in endothelial cells, pericytes and fibroblasts.
Conclusion Our findings indicates the presence of an epitope crossreactive between synovia and the protozoan AP. Epitopes common between micro-organisms and human tissues are possible elements in autoimmunity.
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