[Spondylarthropathies and the IgA system].

The spondyloarthropathies (SA) implicate bacterial infections of mucosal origin. IgA synthesis capacity in vitro is normal in AS. IgA increase is secondary to a specific immune response to the bacterial antigens implicated in the disease's pathogenesis. IgA participate to immune complex formation, which may lead to some extraarticular features of the disease (e.g. renal, cutaneous or vascular). There is also an increase of secretory IgA reflecting the activation of the two compartments of this humoral immune response, part of a coherent pathophysiological scheme of the disease. In a practical point of view, IgA serum levels may be considered as a biological parameter of SA activity.