Objective. Sjögren's syndrome (SS) is an autoimmune condition affecting salivary glands, for which a clearly defined pathogenic autoantibody has yet to be identified. Autoantibodies that bind to the muscarinic M 3 receptors (M 3 R), which regulate fluid secretion in salivary glands, have been proposed in this context. However, there are no previous data that directly show antisecretory activity. This study was undertaken to investigate and characterize the antisecretory activity of anti-M 3 R. Methods. Microfluorimetric Ca 2؉ imaging and patch clamp electrophysiologic techniques were used to measure the secretagogue-evoked increase in [Ca 2؉] i and consequent activation of Ca 2؉ -dependent ion channels in individual mouse and human submandibular acinar cells. Together, these techniques form a sensitive bioassay that was used to determine whether IgG isolated from patients with primary SS and from control subjects has antisecretory activity.Results. IgG (2 mg/ml) from patients with primary SS reduced the carbachol-evoked increase in [Ca 2؉ ] i in both mouse and human acinar cells by ϳ50%. IgG from control subjects had no effect on the Ca 2؉ signal. Furthermore, the inhibitory action of primary SS patient IgG on the Ca 2؉ signal was acutely reversible. We repeated our observations using rabbit serum containing antibodies raised against the second extracellular loop of M 3 R and found an identical pattern of acutely reversible inhibition. Anti-M 3 R-positive serum had no effect on Ca 2؉-dependent ion channel activation evoked by the direct intracellular infusion of inositol 1,4,5-triphosphate.Conclusion. These observations show for the first time that IgG from patients with primary SS contains autoantibodies capable of damaging saliva production and contributing to xerostomia. The unusual but not unprecedented acute reversibility of the effects of anti-M 3 autoantibodies is the subject of further research.

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.

Congenital heart block (CHB) has been linked with Sjögren's Syndrome. This paper reports a case of previously undiagnosed maternal Primary Sjögren's Syndrome (1 degrees SS) that was only discovered following the birth of the patient's first child with CHB. The possible pathophysiological mechanisms underlying CHB associated with 1 degrees SS are discussed.

The severity of salivary gland hypofunction does not appear to be related to the clinical variant of Sjögren's syndrome.

The severity of salivary gland hypofunction does not appear to be related to the clinical variant of Sjögren's syndrome.