Evidence for antimuscarinic acetylcholine receptor antibody-mediated secretory dysfunction in nod mice

Objective. Antibodies directed against general and specific target-organ au toantigens are present in the sera of human patients and animal models with autoimmune disease. The relevance of these autoantibodies to the disease p rocess remains ambiguous in most cases, In autoimmune exocrinopathy (Sjogre n's syndrome), autoantibodies to the intracellular nuclear proteins SSA/Ro and SSB/La, as well as the cell surface muscarinic cholinergic receptor (M- 3) are observed, To evaluate the potential role of these factors in the los s of secretory function of exocrine tissues, a panel of monoclonal and poly clonal antibodies was developed for passive transfer into the NOD animal mo del, Methods. Monoclonal antibodies to mouse SSB/ La, rat M-3 receptor, and a ra bbit polyclonal anti-parotid secretory protein antibody were obtained for t his study, These antibody reagents were subsequently infused into NOD-scid mice. Saliva flow rates were subsequently monitored over a 72-hour period, Submandibular gland lysates were examined by Western blotting for alteratio n of the distribution of the water channel protein aquaporin (AQP), Results, Evaluation of the secretory response indicated that only antibodie s directed toward the extracellular domains of the M-3 receptor were capabl e of mediating the exocrine dysfunction aspect of the clinical pathology of the autoimmune disease. In vitro stimulation with a muscarinic agonist of submandibular gland cells isolated from mice treated with anti-M, antibody, but not saline or the isotype control, failed to translocate AQP to the pl asma membrane. Conclusion. These findings define a clear role for the humoral immune respo nse and the targeting of the cell surface M-3 signal transduction receptor as primary events in the development of clinical symptoms of autoimmune exo crinopathy, Furthermore, the anti-M-3, receptor activity may negatively aff ect the secretory response through perturbation of normal signal transducti on events, leading to translocation of the epithelial cell water channel.