To study local cellular immune reactions in the pleural fluid of patients with rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE).
Using an immunoenzymometric assay, the concentration of soluble interleukin 2 receptor (sIL-2R) was measured in the pleural fluid of 13 patients with RA, 6 patients with SLE and 72 patients with pleural effusions of other etiologies, including tuberculosis, cancer, pneumonia and congestive heart failure.
The mean pleural fluid sIL-2R concentration was significantly higher in patients with RA (593 pM, range 252-1558) than in patients with SLE (145 pM, range 94-236; p < 0.005), cancer (224 pM, range 98-521, p < 0.01), pneumonia (177 pM, range 60-343, p < 0.005) and congestive heart failure (139 pM, range 56-228, p < 0.005), but as high in patients with tuberculous pleurisy (mean 390 pM, range 151-512). The highest mean pleural fluid to serum sIL-2R ratios were observed in patients with RA and with tuberculosis.
Measurement of sIL-2R in pleural fluid is useful for the differentiation of pleural effusions in RA from those occurring in SLE. High levels of sIL-2R associated with a local T cell mediated immune reaction may serve an immunoregulatory purpose in rheumatoid pleurisy.