Serum levels of erythropoietin and the immune parameters tumour necrosis factor-alpha, soluble interleukin-2 receptor, interleukin-2, interleukin-6 and interferon-gamma were measured in patients with rheumatoid arthritis. 2. Out of 69 patients, 44 had anaemia with serum haemoglobin concentrations of 10.8 (SD 1.2) g/dl. In these patients erythropoietin levels were significantly higher than in non-anaemic patients [51.97 (SD 23.9) versus 26.06 (SD 11.9) m-units/ml; P < 0.0001; control patients: 18.1 (SD 13.8) m-units/ml]. Mean soluble interleukin-2 receptor activity was elevated in all patients with rheumatoid arthritis [1324 (SD 715) units/ml; control patients: 480 (SD 75) units/ml; P < 0.001] and was significantly higher in the anaemic group than in the non-anaemic group [1562 (SD 662) versus 696 (SD 402) units/ml; P < 0.0001]. The serum activity of soluble interleukin-2 receptor showed an inverse correlation with haemoglobin (r = 0.79; P < 0.0001) and a positive correlation with erythropoietin (r = 0.70, P < 0.0001). 3. Elevated serum tumour necrosis factor-alpha levels were found in 19 anaemic patients [20.6 (SD 9.1) pg/ml]. Concentrations of tumour necrosis factor-alpha in serum showed an inverse correlation with haemoglobin (r = 0.57, P < 0.001) and a positive correlation with erythropoietin (r = 0.46, P < 0.05). Interleukin-6 was detected in seven anaemic patients [21 (SD 14) pg/ml] and interleukin-2 activity in three anaemic patients (12, 16 and 14 units/ml, respectively). Interferon-gamma was not detected in any of the patients investigated.(ABSTRACT TRUNCATED AT 250 WORDS)
