Autoantibodies in silicosis patients and in silica-exposed individuals

The aim of this study was to evaluate the prevalence of autoantibodies in silica-exposed patients with and without silicosis and without any known rheumatic disease. We studied 61 males exposed to silica for a mean time of 12.2 +/- 10.2 years of exposure. A total of 72.1% (44/61) of them presented with pulmonary silicosis. As control group we included 62 healthy males. In all samples we screened for rheumatoid factor (latex agglutination), antinuclear antibodies (indirect immunofluorescence), anti Scl-70 (ELISA) and ANCA (indirect immunofluorescence technique). One patient (1.6%) of the silica group had weakly positive ANA (titer 1:80, centromeric pattern); one (1.6%) had atypical ANCA and seven patients (11.4%) presented positive rheumatoid factor (values range from 8 to 32 UI/ml). One control patient had a positive RF and none of them had positive ANA or ANCA. All patients and controls were negative for anti-Scl-70. The finding of positive RF was higher in the silica-exposed patients (p = 0.032; Fisher). All patients with positive RF had pulmonary silicosis. In the silica-exposed group we could not find a relationship between the presence of RF and age (p = 0.21; Mann-Whitney), smoking habits (p = 0.25; Fisher) but a positive relationship was found with exposure time to silica dust (p = 0.005; Mann-Whitney). We conclude that there was 11.4% prevalence of low titer RF in the silica-exposed patients without known rheumatic disease. RF was more common in patients with longer exposure to silica dust and appeared only in those with silicosis. The presence of ANA, Scl-70 and ANCA was the same as in the control population.