Human primary Sjogren's syndrome autoantibodies as mediators of nitric oxide release coupled to lacrimal gland muscarinic acetylcholine receptors

IgG obtained from sera of primary Sjogren's syndrome (pSS-IgG) patients and its interaction with M-3 muscarinic cholinoceptors of rat exorbital lacrim al glands were studied by indirect immunofluorescence (IFI) and binding ass ay. Primary Sjogren's syndrome IgG stained epithelial cells with a continuo us fluorescence pattern. The IFI imagen was attenuated by incubating the pS S-IgG with a synthetic peptide corresponding to the second extracellular lo op of M3 muscarinic cholinoceptor. Primary SS-IgG was also able to bound ir reversibly to muscarinic acetylcholine receptors (mAChRs) displacing the sp ecific cholinergic antagonist QNB. Moreover, these antibodies triggered int racellular signals coupled to M-3 muscaric cholinoceptors such as nitric ox ide synthase (NOS) activation and cGMP production. Both primary Sjogren's s yndrome IgG effects mimicked carbachol action and were abrogated by specifi c muscarinic antagonist 4-DAMP. The nitric oxide pathway through muscarinic cholinoceptors activation by pSS-IgG on rat exorbital lacrimal gland is al so described. We proposed that chronic interaction of these autoantibodies on lacrimal gland muscarinic acetylcholine receptors could lead to tissue d amage through nitric oxide release after immunological stimulation.