Rheumatology Advance Access originally published online on September 7, 2004
Rheumatology 2004 43(12):1488-1495; doi:10.1093/rheumatology/keh389
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Rheumatology Vol. 43 No. 12 © British Society for Rheumatology 2004; all rights reserved
PAPER |
Putative anti-muscarinic antibodies cannot be detected in patients with primary Sjögren's syndrome using conventional immunological approaches
The University of Liverpool, Clinical Dental Sciences, Liverpool, UK.
Correspondence to: L. J. Dawson. E-mail: ldawson{at}liv.ac.uk
Objective. To determine whether autoantibodies directed against muscarinic M3 receptors are present in the serum of patients with primary Sjögren's syndrome (pSS), and if so whether these autoantibodies inhibit secretion by intact salivary acinar cells.
Methods. IgG was purified by affinity chromatography using protein G from sera collected from 15 patients with pSS. Antibody detection was by Western blotting, whole-cell enzyme-linked immunsorbent assay (ELISA) and immunoblotting. The antisecretory activity of the IgG faction was determined using fura-2 microfluorimetry to measure changes in intracellular Ca2+ activity ([Ca2+]i) in human and mouse salivary gland acinar cells and in Chinese hamster ovary (CHO) cells transfected with human M3 receptors (CHO-M3).
Results. We found no specific M3 receptor recognition by the IgG fraction obtained from pSS patients using either Western blotting or ELISA or immunoblot techniques in which epitope conformation were preserved. Chronic exposure to pSS IgG had no effect on agonist-evoked Ca2+ signals measured in human or mouse submandibular acinar cells or in CHO-M3 cells. However, acute application of IgG from Sjögren's syndrome patients produced a rapidly reversible reduction in the agonist-stimulated elevation in [Ca2+]i.
Conclusion. These data represent the first demonstration of salivary acinar cell inhibition by pSS IgG; however, this inhibition was found to be reversible. Our data also show that pSS IgG binding to M3R cannot be visualized by conventional immunological approaches.
KEY WORDS: Sjögren's syndrome, Anti-muscarinic M3 antibodies, Human salivary acinar cells, Calcium
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