LAUSR

&NA; The relationship between inflammation and formation of reactive oxygen species (ROS) is still not completely understood and excessive inflammatory reaction is attributed to increased yet also to reduced ROS formation. To compare ROS formation in severe and low inflammation, neutrophil oxidative burst was analyzed in rheumatic patients before and during therapy with TNF&agr;‐ or interleukin‐6 receptor‐neutralizing antibodies. Intracellular and extracellular ROS productions were evaluated on the basis of luminol‐ and isoluminol‐enhanced chemiluminescence in isolated peripheral neutrophils. Disease activity score DAS28 and platelet to lymphocyte ratio were used as markers of arthritis activity and the intensity of systemic inflammation. Biological therapy effectively reduced the intensity of inflammation. Of the twenty‐six patients studied eighteen achieved remission or low disease activity. Highly active arthritis persisted only in one patient, though prior to the therapy it was evident in all subjects tested. In patients receiving biological therapy, intracellular chemiluminescence was significantly higher than in patients before this therapy; ROS produced by neutrophils extracellularly were not affected. The increased ROS formation associated with reduced inflammation supports the need to revise the view of the role of ROS in inflammation ‐ from toxic agents promoting inflammation towards a more complex view of ROS as regulators of immune pathways with inflammation‐limiting capacity. From this perspective, the interference with neutrophil‐derived oxidants may represent a new mechanism involved in the anti‐inflammatory activity of biological therapy.