Salivary IgA and IgG antibodies to bullous pemphigoid 180 noncollagenous domain 16a as diagnostic biomarkers in mucous membrane pemphigoid

Summary Background Mucous membrane pemphigoid ( MMP ) is an uncommon mucocutaneous immunobullous disorder. Use of saliva for diagnosis by enzyme‐linked immunosorbent assay ( ELISA ) using the noncollagenous ( NC ) domain 16a of bullous pemphigoid antigen II ( BP 180) is not well described. Objective To establish whether whole or parotid saliva is a suitable alternative to serum for diagnosis of MMP . Methods Precoated BP 180‐ NC 16a ELISA plates were used to test serum, and whole and parotid saliva for IgG, IgA and secretory IgA antibodies. Patients with MMP ( n = 64) provided matched serum and whole saliva. In addition 18 of the MMP patients also provided matched parotid saliva. Healthy controls ( n = 50) provided matched serum and whole saliva and 6 of these additionally provided matched parotid saliva. An additional 16 disease controls provided matched serum, and whole and parotid saliva. Results In whole saliva, IgG antibodies were detected in 11/64 (17%), IgA in 23/64 (36%) and a combined positivity in 29/64 (45%). In parotid saliva, IgA antibodies were found in 8/18 (44%). Serum IgG antibodies were detected in 27/64 (42%), serum IgA antibodies in 18/64 (28%) and a combined positivity in 33/64 (52%). Combined use of serum and saliva increased detection of specific antibodies by 30%. Control samples were all negative (positive predictive value of 100% for all tests). The negative predictive values were 62% for IgA saliva, 65% for IgG serum, 59% for IgA serum and 56% for IgG saliva. Conclusions IgG and IgA antibodies may provide a suitable diagnostic marker in MMP . Assay of salivary IgA antibodies to NC 16a offers a similar diagnostic predictive value to serum.