Does Detectable Anti-muscarinic-acetylcholine Type-3 Receptor Autoantibody Correlate with Sjögren's Syndrome?

Objective: The presence of circulating autoantibodies, especially anti-SS-A/Ro, anti-SS-B/La and ANAs, represents important criteria in the identification and diagnosis of Sjögren's syndrome (SjS), despite the fact that these are not specific to the disease. Recent studies from our laboratory have suggested that antibodies reactive with the muscarinic acetylcholine type-3 receptor (M3R) may correlate with the loss of secretory function leading to dry mouth/dry eye disease. This study investigates whether the presence of anti-M3R antibodies is useful as a diagnostic.

Methods: Nearly 200 sera collected from SjS patients and controls (from Dr. Roland Jonsson, Bergen) were assayed by flow cytometry using human-M3R-transfected Flp-In CHO cells. Cells were incubated with either patient or control whole sera, washed and stained with FITC-conjugated donkey anti-human IgG or FITC-conjugated mouse anti-human IgG, IgG1, IgG2, IgG3, IgG4, IgA1, IgA2 or IgM. Samples were analyzed using a FACScan cytometer (Becton Dickonson).

Results: Of the 83 SjS patients, 30% showed strong positive staining, 34% weakly positive staining and 36% negative staining. In contrast, of the 11 SLE patients, 9% showed strong positive staining, 36% weakly positive staining and 55% negative staining. Normal healthy controls (n=94) exhibited 20% strong positive staining, 43% weak positive staining and 37% negative staining. Subclass analyses revealed positive staining primarily with IgG1 and IgG3, but no positive with IgG4. There was an unexpectedly high positive staining by IgM subclass antibodies from control sera that may impact on the overall results.

Conclusions: At this time, we have found relatively minor differences in the staining of human-M3R-transfected Flp-In CHO cells by sera from SjS and non-SjS controls. Further analyses are required to identify the non-specificity observed thus far, for which a good control antibody (commercial or otherwise) would be critical.

Supported by NIH grant AI47483