CIRCULATING ANTIBODIES AGAINST RAT PAROTID-GLAND M(3) MUSCARINIC RECEPTORS IN PRIMARY SJOGRENS-SYNDROME

In this study we demonstrate that IgG present in the sera of patients with primary Sjogren's syndrome (PSS) could bind and activate muscarin ic acetylcholine receptors (mAChRs) of rat parotid gland. These antibo dies were able to inhibit in a non-competitive manner the binding of H -3-quinuclidinyl benzilate (QNB) to mAChRs of purified rat parotid gla nd membranes. Moreover, IgG from PSS could modify biological effects m ediated by mAChR activation; i.e. decrease cAMP, increase phosphoinosi tide turnover without affecting cGMP. Atropine and 4-DAMP blocked all of these effects, and carbachol mimicked them, confirming the M(3) sub type mAChRs mediated PSS IgG action. Neither binding nor biological ef fect were obtained with Ige From sera of normal women. The prevalence of cholinergic antibody was 100% in PSS, and was independent of Ro/SS- A and La/SS-B antibodies. Ir could be concluded that antibody against mAChRs mag. be another scrum factor to be considered in the pathophysi ology of the development of PSS.