Effect of antimuscarinic autoantibodies in primary Sjögren's syndrome

The presence of functional autoantibodies against the muscarinic type 3 receptor (m3r) has been reported in primary sjögren's syndrome (pss). however,the pathogenic role of these autoantibodies in pss development remains to be elucidated. in this experiment,we investigated a pathologic role of pss autoantibodies (pss igg) associated with downregulation of the major histocompatibility complex i (mhc i) molecule with m3r through internalization. anti-m3r autoantibodies in purified control and pss igg were detected using 4 synthesized cyclic m3r peptides by enzyme-linked immunosorbent assay. the binding reactivity of pss igg to m3r in situ was analyzed by a dual immunostaining method. surface expression,interaction,and internalization of m3r with mhc i were analyzed by immunofluorescence confocal microscopy and biochemical assays. synthetic cyclic peptides m3rp205-221 and m3rp520-527 showed significantly high reactivity with pss igg compared to the control igg or the other 3 peptides (p < 0.05). significantly high reactivity of pss igg to m3r in situ was observed. pss igg increased the interaction of membrane m3r with mhc i and induced their internalization in primary human submandibular gland cells. the pss igg-induced internalization of m3r with mhc i was significantly inhibited by the cholesterol-sequestering drug filipin. our novel finding - namely,strong downregulation of the membrane mhc i with m3r through internalization of the cholesterol-rich microdomain associating with anti-m3r autoantibodies - could be an important mechanism contributing to the impaired salivation seen in pss and linking secretory hypofunction to autoimmune pathogenesis. © 2015 international & american associations for dental research.