Detection of autoantibodies against aquaporin-5 in the sera of patients with primary Sjögren’s syndrome

Abstract

The pathophysiology of exocrine dysfunction observed in Sjögren’s syndrome (SS) is not fully understood. The purpose of this study was to investigate whether autoantibodies against human AQP5 are present in the sera of SS patients. Frozen sections of mouse submandibular salivary glands, CHO cells over-expressing a human AQP5–GFP fusion protein or GFP, and MDCK cells over-expressing AQP5 were used in the indirect immunofluorescence assay to detect anti-AQP5 autoantibodies in the sera from patients with primary SS. The lysates of HEK-293 cells over-expressing the AQP5–GFP fusion protein or GFP were used for immunoprecipitation. Serum IgG from the SS patients but not from the control subjects stained acinar cells in the mouse salivary glands, the signals of which colocalized with those of AQP5-specific antibodies. Serum IgG from the SS patients also selectively stained AQP5–GFP expressed in CHO cells. However, both the control and SS sera immunoprecipitated the AQP5–GFP, suggesting that autoantibodies against AQP5 were also present in the control sera. The screening of 53 control and 112 SS samples by indirect immunofluorescence assay using the AQP5-expressing MDCK cells revealed the presence of significantly higher levels of anti-AQP5 IgG in the SS samples than in the control samples with sensitivity of 0.73 and a specificity of 0.68. Furthermore, the presence of anti-AQP5 autoantibodies was associated with low resting salivary flow in SS patients. In conclusion, anti-AQP5 autoantibodies were detected in the sera from SS patients, which could be a novel biomarker of SS and provide new insight into the pathogenesis of SS.Electronic supplementary materialThe online version of this article (doi:10.1007/s12026-016-8786-x) contains supplementary material, which is available to authorized users.

Dysbiotic oral microbiota and infected salivary glands in Sjögren’s syndrome

“…To investigate potential roles of the SS-associated species in the pathogenesis of SS, we tested in vitro if selected species of oral bacteria could induce functional and phenotypic changes in SGECs. Three SS-associated bacterial species were selected among the species that are top 30 abundant and contain aquaporins (AQPs) or porins homologous to human AQP 5 [25]: P. histicola, a species associated with SS in both non-dry and dry conditions; and P. melaninogenica and R. mucilaginosa, species associated with SS in the non-dry condition. S. salivarius, the most abundant commensal species in saliva, and F. nucleatum, a highly immune stimulatory species, were additionally included as negative and positive controls, respectively.…”

“…The titers and the local production of anti-SSA and anti-SSB autoantibodies were significantly increased in patients with GC development [41]. The presence of bacteria in the GC-like structures may contribute to the proliferation of B cells and the production of autoantibodies, including anti-AQP5 autoantibodies [25], at local sites through direct stimulation of TLR4 and TLR9 or through exosomes produced from the infected cells. One unanswered question is how neutrophils are not recruited in the presence of bacteria.…”

Detection of Autoantibodies against Aquaporin-1 in the Sera of Patients with Primary Sjögren's Syndrome

“…Previously, we reported a high degree of homology between AQP5 and AQPZ or porins from many human-associated bacteria, including the members of normal human oral flora (18). The same oral bacterial AQPs presented 35~42% identity and 52~56% similarity with AQP1 (Fig.…”

Aquaporin-Targeted Therapeutics: State-of-the-Field

“…Though it was initially proposed from oocyte swelling studies that inhibition of AQP4 water permeability plays a causal role in NMO [11], subsequent studies showed that AQP4-IgGs, even at saturating concentrations, do not inhibit AQP4 water permeability [30]. Interestingly, autoantibodies against AQP2 [17] and AQP5 [1] have been found recently in interstitial nephritis and Sjogren’s syndrome, respectively, though their involvement in disease pathogenesis is not known.…”