The microvascular localization of laminin and fibronectin in scleroderma muscle by immune electron microscopy

Immune electron microscopy using a peroxidase-antiperoxidase (PAP) technique was done on muscle biopsies from patients with scleroderma (PSS), rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and normal controls, in order to localize laminin and fibronectin in the muscle capillary basement membrane (BM). Three patterns of staining were noted for the 2 antigens: in/out, diffuse and negative. Staining patterns in PSS biopsies were markedly different from both the normal and disease controls. For laminin the expected in/out pattern was rare in PSS, with virtually all biopsies being either diffuse or negative. In the case of fibronectin, the staining patterns were of equal frequency in PSS, whereas in the control groups diffuse staining was rare. These findings suggest that in addition to the morphologic abnormalities previously noted in PSS muscle capillary BM, there is also an alteration in the distribution of specific BM components in PSS.