No evidence of increased anti‐M3 muscarinic acetylcholine receptor autoantibodies in SSA‐positive connective tissue disease patients

Anti‐muscarinic type 3 receptor autoantibodies (M3R) and anti‐SSA antibodies are both related to salivary secretion. The presence of M3R antibodies in Sjögren's syndrome is previously demonstrated; nevertheless, the relationship between the anti‐SSA antibodies and M3R fragment antibodies, namely the N terminal, first, second, and third extracellular loops, remains to be elucidated. In this study, we analyzed the antibodies against the M3R epitopes in healthy controls and anti‐SSA antibody‐positive connective tissue disease patients through ELISA method. Antibodies against the first, second, and third extracellular loop (M3R211–230) were not increased in anti‐SSA positive patients compared to healthy controls. Indeed, antibodies against the N terminal (M3R1–33) were found to be high in healthy controls. High levels of M3R1–33 in healthy controls are a novel original finding; further research is needed for the clinical significance. There is no significant difference between SSA‐positive patients and healthy controls in terms of autoantibodies against the remainder of the linear M3R fragments.