Raised circulating levels of the eosinophil cationic protein in ankylosing spondylitis: relation with the inflammatory activity and the influence of sulphasalazine treatment.

The possibility of eosinophil involvement in ankylosing spondylitis (AS) was investigated by measuring serum levels of eosinophil cationic protein (ECP), a specific granule constituent of eosinophils. In a group of 48 patients with AS we found a threefold increase of the mean serum levels of ECP compared with a reference group (p less than 0.001). The blood eosinophil counts were similar in patients and controls. A correlation was found between ECP and inflammatory activity defined by erythrocyte sedimentation rate (ESR) and serum haptoglobin. Fifteen patients were studied before and after three months' treatment with sulphasalazine (2-3 g/day). The ECP levels decreased in 13/15 and this paralleled reduction of the acute phase reaction and improvement of clinical parameters. The results point to eosinophil activation as part of the inflammatory process in AS. The signs of reduced eosinophil activation during sulphasalazine treatment suggest either a drug mediated, direct effect on eosinophils or an effect on the inflammatory mechanism stimulating eosinophils.