Immunoglobulin synthesis by peripheral blood lymphocytes in patients with ankylosing spondylitis.

Immunoglobulin synthesis by peripheral blood lymphocytes and serum IgA subclasses were investigated in patients with ankylosing spondylitis (AS) with and without accompanying microscopic hematuria, and HLA-B27 positive and negative healthy controls. An increase in serum IgA, restricted to subclass IgA1, was found in patients with AS, especially in those with microscopic hematuria. IgA synthesis was not increased, but a significant shift to subclass IgA1 was found. Our results resemble abnormalities previously noted in primary IgA nephropathy, and further support the pathogenetic role of IgA in AS.