Inhibitory effects of muscarinic receptor autoantibodies on parasympathetic neurotransmission in Sjögren's syndrome

Abstract

Objective. Sjögren's syndrome (SS) is an autoimmune disorder characterized by dry eyes and mouth (sicca syndrome) and lymphocytic infiltration of the lacrimal and salivary glands. Abnormalities of parasympathetic neurotransmission may contribute to the glandular dysfunction. In this study, we used a functional assay to investigate autoantibody-mediated effects on parasympathetic neurotransmission and smooth muscle contraction.Methods. Serum and purified IgG were obtained from patients with primary and secondary SS and from control subjects. Contraction of isolated bladder strips in response to stimulation of M 3 -muscarinic receptors by a muscarinic receptor agonist, carbachol, or by endogenous acetylcholine released from postganglionic parasympathetic nerves was measured before and after the addition of patient serum or IgG.Results. Sera from 5 of 9 patients with primary SS and from 6 of 6 patients with secondary SS inhibited carbachol-evoked bladder contraction by ϳ50%. Sera from these patients also inhibited the action of neuronally released acetylcholine at M 3 -muscarinic receptors. Sera from 7 of 8 healthy individuals, from patients with rheumatoid arthritis without sicca symptoms, and from patients with systemic lupus erythematosus had no effect. The anti-muscarinic receptor activity was localized in the IgG fraction, since purified IgG from patients with SS also inhibited agonist-and nerve-evoked contractions. In this preliminary study, the autoantibodies seemed to be associated with the presence of bladder symptoms and other autonomic features.Conclusion. Autoantibodies that act as antagonists at M 3 -muscarinic receptors on smooth muscle occur in a subset of patients with primary and secondary SS. Their presence in secondary SS was unexpected and provides new evidence for a common pathogenetic link between primary and secondary SS. These autoantibodies appear to contribute to sicca symptoms and may explain associated features of autonomic dysfunction in some patients.

Antimuscarinic antibodies in Sjögren's syndrome: Where are we, and where are we going?

“…The reversibility of the binding observed when mouse or human submandibular acinar cells are exposed to SS IgG or rabbit polyclonal anti-M 3 R is intriguing since it confirms the previous findings in Ig -null mice (71) but is contradictory with data obtained from smooth muscle bioassay (15,62,64) and radioligand binding studies (14,73). In myasthenia gravis it is established that, in vitro, the reversibility of the interaction between the autoantibodies and the nicotinic cholinergic receptors is highly dependent on the length of time of exposure and the concentration of the autoantibody (85).…”

“…Although SS is classified as an autoimmune disease, no specific pathologic autoantibody has been found (3,13). However, data from recent studies have suggested that patients with primary SS and patients with secondary SS may have inhibitory autoantibodies directed against muscarinic receptors (14)(15)(16). The presence of inhibitory autoantibodies directed against salivary gland muscarinic receptors would serve to unite the pathologies underlying the glandular hypofunction of both primary and secondary SS, explaining why the degree of glandular hypofunction is equivalent in the two (17).…”

Inhibitory effects of autoantibodies on the muscarinic receptors in Sjögren's syndrome

“…23 Likewise, persistent loss of sensitivity to Ach was reported in salivary acinar cells that obtained from SS patients. 24 Interestingly, SS IgG induced a similar degree of inhibition in the CChevoked bladder contraction by approximately 50%, 25 suggesting that CICT is also reduced in this tissue, because [Ca 2 þ ] i also plays a putative role in smooth muscle contractions.…”

Up-regulation of M3-Muscarinic Receptors in Labial Salivary Gland Acini in Primary Sjögren's Syndrome

“…In human salivary glands, binding of anti-M3R autoantibodies (Nguyen et al 2000;Waterman et al, 2000) would initially be expected to cross-link receptors and trigger internalization and a decrease in receptor number. However to compensate for this short-term change, an increase in receptor density appears to occur (present study).…”

“…Dawson et al (2001) demonstrated changes consistent with receptor down-regulation: a decrease in muscarinic receptor sensitivity in salivary acinar cells with no change in the maximal response to muscarinic receptor stimulation. Functional anti-muscarinic receptor antibodies have been demonstrated in the serum of patients with primary Sjögren's syndrome (pSS) and these inhibit parasympathetic neurotransmission (Waterman et al, 2000). Such an inhibition of neurotransmission might be predicted to cause a compensatory up-regulation of M3R number.…”