There have been several reports on the fine structure of the synovial membrane in rheumatoid arthritis.All have stressed the cytoplasmic dense bodies which characterize the type A lining cell, but none have mentioned intranuclear bodies (Barland, Novikoff, and Hamerman, 1969; Hirohata and Kabayashi, 1964;Norton, Lewis, and Ziff, 1966; Marin, Negoescu, Stoia, Pierette, Petrescu, and Constinescu, 1969). Our own studies, however, have revealed characteristic nuclear inclusions in rheumatoid synovial membrane. In the present paper we describe and illustrate these, and discuss their possible significance.Material and methods Synovial membrane was obtained from 22 patients with rheumatoid arthritis during synovectomy of the knee which was carried out under spinal anaesthesia. The ages of the patients ranged from 20 to 69 years. The disease had been present in all of them for several years. Seven were strongly positive for the latex-fixation test. Ten had been treated with prednisolone*, 15 to 45 mg./day for from 9 months to 5 years.Control specimens were obtained from six nonrheumatoid patients who were undergoing meniscectomy, or were being operated on for fracture of the patella. Needle biopsies of the peristriate area of the right cerebral cortex of eight patients suffering from subacute sclerosing encephalitis, a condition known to be associated with nuclear inclusions containing the helical components of measles virus (Adels, Gajdusek, Gibbs, Albrecht, and Rogers, 1968;Waterson, 1965; Tellez-Nagel and Harter, 1966b) were also studied.After excision, specimens were immediately flooded with buffered Karnovsky fluid at pH 7 2 (Karnovsky, 1965) and then immersed for 1 hour in buffered 1 per cent. osmium tetroxide. After dehydration in alcohol, specimens were embedded in Durcupan. t Sections were cut with a Reichert OM-2 ultramicrotome, stained with uranyl acetate and lead citrate according to the method of Reynolds (1963), and examined in a Philips EM-300 electron microscope.
ResultsCharacteristic nuclear bodies were found in all the rheumatoid specimens but in none of the control specimens of synovial membranes. They were mostly located in the endothelial cells and pericytes of capillaries and/or larger vessels beneath the synoviocyte lining layers and in deeper zones. They were also seen less frequently in cells judged to be mononuclear cells. Although ten blocks were taken from every specimen, generally only five showed intranuclear inclusions. In many cases multiple sections were needed to detect the presence of nuclear bodies. However, it was not possible to correlate the number of intranuclear bodies with any of the various clinical findings. Nuclear bodies were not seen in Type A or Type B synoviocytes, lymphocytes, or plasma cells.The most common type of nuclear body is illustrated in Figs la, ic, 2a, 2c, and 3a. It consists essentially of groups of filamentous or tubulo-filamentous structures, often surrounded by a clear halo. In