Lymphopenia in occupational pulmonary silicosis with or without autoimmune disease

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Abstract
An increased prevalence of autoimmune diseases such as rheumatoid arthritis has been demonstrated in silica-exposed patients. The aim of this study was to determine the peripheral blood lymphocyte phenotype in a population of silicotic workers employed in the slate mines of the district. Silicosis was assessed in 58 patients according to the International Labor Office's criteria. Clinical and biological data including flow cytometric evaluation of the lymphocyte subsets were compared with those from 41 healthy volunteers. The silicotic patients had a higher prevalence of autoimmune diseases (6/58 versus 0/41: P < 0·05) and of elevated antinuclear antibody titres compared to the control group. A very significant decrease of total lymphocyte count (P < 0·001) involving B, T and Natural Killer cells was found in silicotic patients as compared with matched healthy volunteers. A significant increase in the percentage of activated T cells (12·3%) was observed in the silicotic group as compared to 6·5% in the control group (P = 5 × 10−5). Our results show that in silicotic patients, the absolute number of circulating lymphocytes is diminished with an increased proportion of activated T cells. Whether these findings could predispose to the development of autoimmune disorders is discussed.