Immunoperoxidase EM localisation of cytoplasmic actin in cultured fibroblasts.

Human smooth muscle autoantibody (SMA) of defined anti-actin specificity was tested by the indirect immunoperoxidase staining method on frozen sections of tissues and on cultured rat lung fibroblasts. The serum stained tissue sections and cultured fibroblasts in a pattern identical with that obtained by indirect immunofluorescence. Ultrastructural studies carried out on the immunoperoxidase stained cells showed that the long parallel filaments spanning the long axis of cultured fibroblasts seen by light microscopy correspond with the thick bundles of microfilaments.

Antibody to intermediate filaments of the cytoskeleton.

IgM antibodies against cultures of intermediate filaments (IMF) of the cytoskeleton were demonstrated by immunofluorescence in the sera of 94 (80%) of 118 patients with seropositive rheumatoid arthritis. These antibodies reacted with IMF in cultures of both human fetal fibroblasts and laryngeal carcinoma (HEp2) cells. Of 10 patients from whom paired synovial fluids were also available 8 had anti-IMF antibodies in both serum and fluid. In seronegative RA the incidence of anti-IMF was 40%, in ankylosing spondylitis 25%, in osteoarthrosis 16%, and in normal subjects 14%. Only a minority of RA sera positive for anti-IMF antibodies were also positive for smooth muscle antibody. Absorption experiments suggest that in RA anti-IMF is directed at the intermediate filament protein, vimentin.

Intermediate filaments in synovial lining cells in rheumatoid arthritis and other arthritides are of vimentin type.

Cryostat section of synovial tissue from patients with rheumatoid arthritis, ankylosing spondylitis, osteoarthrosis, pigmented villonodular synovitis, and from a normal knee were studied by indirect immunofluorescence with guinea-pig antibodies to the intermediate filament proteins prekeratin, vimentin, and desmin. Staining for vimentin, but absence of prekeratin and desmin, was demonstrated in synovial lining cells. Antivimentin antibody also stained synovial tissue fibroblasts and vascular endothelial lining cells. The intensity of fluorescent staining for vimentin broadly correlated with cellular proliferative activity at these 3 sites.