Role of salivary IgA in the pathogenesis of Sjögren syndrome.

Saliva IgA autoantibodies against M(3) muscarinic acetylcholine receptors (mAChRs) could be a new marker for the diagnosis for Sjögren syndrome (SS) dry mouth. Saliva IgA from dry mouth primary SS (pSS) or secondary SS patients tested by ELISA recognized membrane parotid gland acinar cell antigens and the synthetic 25-mer peptide corresponding to the second extracellular loop of human M(3) mAChRs. Moreover, the IgA fraction was able to inhibit the [(3)H]QNB binding to parotid acinar membrane mAChRs. In addition, the IgA prevented carbachol stimulation of protein secretion by the parotid gland. As controls, IgA and saliva from women without dry mouth and from normal control subjects gave negative results on ELISA, binding, and biological assays, thus demonstrating the specificity of the reaction. IgA autoantibodies against mAChR may be considered among the immunoglobulin factors implicated in the pathophysiology of the development of pSS dry mouth and could be a new marker for differentiating SS dry mouth from non-SS dry mouth.