Patients and methods
Blood was obtained from 122 AS patients during varying phases of disease activity. A total of 221 patient sera were randomly selected from a bank of stored sera, each patient being selected on average twice (range 1-5). Each patient visit was considered as 1 separate event, the shortest interval between visits being 1 month. The New York criteria were used for the diagnosis of AS.11 Patients with inflammatory bowel disease were excluded from the study. The mean age of all patients was 34-5 years (range 11-£8), and 29 were women. Of 117 patients tested 110 were HLA B27 positive (94%). Single serum samples were obtained from 58 healthy subjects corresponding in age and sex distribution to the AS patients and who had no history of arthritis or backache.
Serum IgA, IgG, and IgM estimations were determined by the radial immunodiffusion technique with commercially prepared immunodiffusion plates and protein standards (Behringwerke, Mar-burg/Lahn). Blood for the erythrocyte sedimentation rate (ESR) was taken at each patient visit and measured by the Westergren method. Serum C-reactive protein (CRP) estimations were determined by the radial immunodiffusion technique with commercial antisera (Hoechst), and each estimation was the mean of at least 2 separate measurements. All measurements were carried out in code without knowledge of the patient's clinical status.