Substrate specificity of antinuclear antibodies in scleroderma

Studies of antinuclear antibodies (ANA) were carried out in 39 cases of systemic scleroderma and for comparison in 19 cases of systemic lupus erythematosus (SLE) and 4 of mixed connective tissue disease (MCTD) using indirect immunofluorescence (IF) methods under standard conditions. The results on three different substrates--monkey esophagus, guineapig lip and rat liver--are reported. In 48.7% of scleroderma cases ANA showed a substrate specificity. The highest percentage of positive results in scleroderma was obtained on monkey esophagus (97.4%) and the lowest on rat liver (61.5%). In SLE and MCTD, in contrast, only about 13% of the sera displayed such specificity. If only sera with substrate specificity are considered, the positive results on monkey esophagus and rat liver are 94.7% and 21.1%, respectively. Titers of sera reacting positively on 2 or 3 substrates were mostly in agreement, although some sera both in systemic scleroderma and SLE showed higher titers on monkey esophagus. The IF pattern was usually the same regardless of the substrate, Tests for ANA in scleroderma should be performed on at least 2 substrates simultaneously.