Peptide-based ELISAs are not sensitive and specific enough to detect muscarinic receptor type 3 autoantibodies in serum from patients with Sjogren's syndrome

The detection of autoantibodies to the muscarinic receptor type 3 (M3R) in the serum of patients with Sjögrens syndrome (SS) by ELISA is controversial. A study was undertaken to test whether modification of M3R peptides could enhance the antigenicity and increase the detection of specific antibodies using an ELISA. A series of controlled ELISAs was performed with serum from 71 patients with SS and 37 healthy volunteers (HV) on linear, citrullinated and/or cyclised and multi-antigenic peptides (MAP) of the three extracellular M3R loops to detect specific binding. Significant differences (p <0.05) in optical density (OD) between serum from patients and HV were detected for a cyclised loop 1-derived peptide and the negative control peptide. Furthermore, there were no statistically significant differences between the frequency of positive patients (defined as OD >2SDs above the mean of the HV) and HV on any of the peptides tested. Binding of serum from patients with SS to M3R-derived peptides does not differ from binding to a control peptide in an ELISA and no significant binding to M3R-derived peptides was found in the serum from individual patients compared with HV. These data suggest that peptide-based ELISAs are not sufficiently sensitive and/or specific to detect anti-MR3 autoantibodies