SUMMARY
Tumour necrosis factor‐alpha (TNF‐α) is involved in diverse biological processes including immune and inflammatory reactions and the response to surgical stress. Two soluble TNF receptor protein fragments. TNF‐sR55 (from the p55 kD TNF receptor) and TNF‐sR75 (from the p75 kD TNF receptor), are released by cells during inflammation and may modulate the effects of TNF‐α. We have studied the kinetics of secretion of TNF‐α, TNF‐sR55 and TNF‐sR75 in the sera of patients with rheumatoid arthritis (RA) and control subjects with osteoarthritis (OA) or chronic osteomyelitis (OM) before and after major surgery. Significantly higher pre‐operative levels of TNF‐sR55 and TNF‐sR75 were found in RA and OM as compared with OA (P<0.02). Following surgery, TNF‐sR55 increased within 24 h in RA, OM and OA (P<0.05), whereas TNF‐sR75 increased significantly only in OM and OA patients (P<0.05). By contrast, no TNF‐α was detectable before and after surgery in any of the subjects, but this may have been due to impaired detection (by ELISA) of TNF‐α when it is bound to TNF‐sR. These findings suggest that TNF‐sR55 and TNF‐sR75 may be further markers of the host's reaction to inflammatory insults. They may also play a role in modulating the immune and inflammatory reactions by inhibiting the systemic effects of TNF‐α.