Association of inflammation with raised serum IgA in ankylosing spondylitis.

Serum immunoglobulins were measured in 122 patients with ankylosing spondylitis (AS) during various phases of disease activity and compared to those in 58 healthy subjects. The mean serum IgA was 38% higher in patients (306.9 mg/dl) than in controls (222.7 mg/dl) (P < 0.005), but there was no significant difference in IgG and IgM levels. Increased IgA was associated with laboratory parameters of active inflammatory disease. The mean IgA in patients having an erythrocyte sedimentation rate (ESR) equal to or greater than 15 mm/h was 369 mg/dl, 65% higher than in controls (P < 0.001), whereas there was no significant difference between controls and patients with an ESR of less than 15 mm/h. The mean IgA in patients having a C-reactive protein (CRP) level equal to greater than 15 micrograms/ml (15 mg/l) was 387.8 mg/dl, 74% higher than in controls (P < 0.001), and again there was no significant difference between controls and patients with CRP levels less than 15 micrograms/ml. (SI conversion: g/l = mg/dl x 0.01). It is suggested that selective increase of serum IgA occurs predominantly during phases of active inflammatory disease in AS, and this finding is compatible with the concept of a microbial triggering agent acting across an IgA secreting organ such as the gut.