Antinucleolar autoantibodies demonstrated by monolayers of human fibroblasts in sera from patients with systemic lupus erythematosus, progressive systemic sclerosis and chronic active hepatitis.

Antinucleolar antibody (ANoAb) was tested for in sera from 25 patients with systemic lupus erythematosus (SLE), 61 with progressive systemic sclerosis (PSS), 22 with chronic active hepatitis (CAH) and 28 healthy persons, using immunofluorescence reactivity with acetone-fixed monolayers of cultured human fibroblasts, and a procedure to reveal ANoAb when other antinuclear antibodies were concurrently present. ANoAb was found on direct testing in sera from 6 patients with SLE, 15 with PSS and 7 with CAH, but not in any of 28 sera from healthy persons; homogeneously reactive antinuclear antibody was also present in the serum of these 6 cases of SLE, in 6 of the 15 with PSS and in 3 of the 7 with CAH and, in SLE specifically, pre-treatment of fibroblast monolayers with DNase "unmasked" the presence of ANoAb in a further 7 sera which had shown only homogeneous nuclear staining in fibroblasts. ANoAb belonged to the IgG, IgM and IgA class in sera from cases of SLE and PSS, and to only the IgG and IgM class in sera from cases of CAH. ANoAb titres were highest in patients with PSS. ANoAb were sensitive to RNase in 5 cases, to RNase and DNase in 6, and were sensitive to combinations of RNase, DNase, NaC1, and trypsin in the remaining cases. We conclude that (i) fibroblast monolayers are a suitable substrate for the demonstration of ANoAb, (ii) homogeneous staining of cell nuclei may mask ANoAb, so that the incidence of ANoAb becomes higher in SLE than in PSS, (iii) low-titre ANoAb in CAH not visualized in frozen tissue sections may be detected on fibroblast monolayers, and (iv) nucleolar antigens probably include RNA, RNA bound to DNA, and RNA bound to proteins.