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 lacrimal glands were studied by indirect immunofluorescence (IFI) and binding assay. Primary Sjogren's syndrome IgG stained epithelial cells with a continuous fluorescence pattern. The IFI imagen was attenuated by incubating the pSS-IgG with a synthetic peptide corresponding to the second extracellular loop of M3 muscarinic cholinoceptor. Primary SS-IgG was also able to bound irreversibly to muscarinic acetylcholine receptors (mAChRs) displacing the specific cholinergic antagonist QNB. Moreover, these antibodies triggered intracellular signals coupled to M-3 muscaric cholinoceptors such as nitric oxide synthase (NOS) activation and cGMP production. Both primary Sjogren's syndrome IgG effects mimicked carbachol action and were abrogated by specific muscarinic antagonist 4-DAMP. The nitric oxide pathway through muscarinic cholinoceptors activation by pSS-IgG on rat exorbital lacrimal gland is also described. We proposed that chronic interaction of these autoantibodies on lacrimal gland muscarinic acetylcholine receptors could lead to tissue damage through nitric oxide release after immunological stimulation.