AQP5 antibody named potential diagnostic biomarker in primary Sjögren’s
Combo using anti-AQP5 may 'enhance' disease's diagnostic rate: Study
Blood levels of antibodies against aquaporin 5 (anti-AQP5) — a protein that regulates water movement in tissues — may be used as a biomarker to diagnose primary Sjögren’s disease, a study from researchers in China suggests.
The presence of anti-AQP5 antibodies has been associated with reduced saliva production in some people with Sjögren’s. Criteria for diagnosing Sjögren’s disease now include detecting antibodies known as anti-SSA and anti-SSB, but not anti-AQP5.
However, accuracy with current testing is problematic, “falling short of clinical requirements” in both sensitivity and specificity, the researchers noted. Sensitivity measures how well a test can identify people with a disease, while specificity determines how well it identifies those without it.
According to the team, “the study reveals that anti-AQP5 possess higher sensitivity compared to anti-SSA antibody, potentially compensating for the limited detection rate of anti-SSA antibody in [Sjögren’s disease] patients.”
Thus, “combining the use of anti-AQP5 could enhance the diagnostic rate of [Sjögren’s disease],” the researchers wrote.
The study, “Autoantibody against aquaporin-5 may be a new diagnostic biomarker for primary Sjögren’s syndrome,” was published in Clinical Rheumatology.
Anti-AQP5 antibody found to be significantly higher in Sjogren’s patients
Sjögren’s disease is an autoimmune condition that primarily affects the glands that produce tears and saliva, leading to eye and mouth dryness, although other organs may be affected. It is classified as primary Sjögren’s when it appears isolated, and as secondary if it follows another autoimmune disease.
The condition is caused by the presence of autoantibodies — most commonly anti-SSA and anti-SSB — that prompt an inflammatory response against the body’s tissues. Other autoantibodies, such as those targeting aquaporins, or AQPs, have also been identified in people with Sjögren’s.
Now, researchers from the Army Medical University, also called the Third Military Medical University, in Chongqing evaluated data from 63 people with primary Sjögren’s to investigate whether anti-AQP1 and anti-AQP5 antibodies could be potential biomarkers of the disease. The patients’ data was collected between September 2021 and January 2022.
Another 61 individuals with other connective tissue diseases, including rheumatoid arthritis, lupus, and systemic sclerosis, served as controls, as did 39 healthy individuals. The Sjogrën’s patients were mostly women (92.1%) and had a mean age of 47.9 years.
Levels of anti-AQP1 antibodies were found to be significantly higher in people with Sjögren’s — 27.2 nanograms (ng)/mL — or with other diseases (27.3 ng/mL) as compared with the healthy controls (24.4 ng/mL). However, there were no significant differences when comparing the two groups of patients.
Regarding anti-AQP5 antibodies, their levels were significantly higher in Sjogren’s patients compared with both the individuals with other diseases and the healthy controls (26.4 vs. 9.1 vs. 5.9 ng/mL). The levels of both types of antibodies were not correlated with disease activity, according to the EULAR Sjögren’s syndrome disease activity index.
The diagnostic significance of both antibodies was assessed using a measure called area under the curve, or AUC, a test of how successful the differentiation of two groups is. AUC values range from 0.5 to 1, with higher values indicating a better ability to tell two groups apart.
The results showed that anti-AQP5 antibody levels above 14.1 ng/mL were able to diagnose Sjögren’s with an AUC of 0.98. Its sensitivity was 97%, whereas specificity was 100%.
[Overall,] anti-AQP5 levels significantly increased in [primary Sjögren’s disease] patients …. indicating that anti-AQP5 is a novel diagnostic biomarker.
When patients with other conditions were used as controls, anti-AQP5 levels above 18.8 ng/mL were able to diagnose Sjögren’s with an AUC of 0.86, a sensitivity of 95%, and a specificity of 70%.
Additional analyses indicated that anti-AQP5 was not correlated with the levels of other autoantibodies, including anti-SSA, anti-SSB, or antinuclear antibodies. It also did not correlate with the salivary gland flow rate.
Overall, “anti-AQP5 levels significantly increased in [primary Sjögren’s disease] patients …. indicating that anti-AQP5 is a novel diagnostic biomarker,” the researchers wrote.
However, more research is needed, per the team.
“Further prospective studies in large-size multicenter cohorts and diverse experimental methods are needed to validate the diagnostic advantage of the AQP5 antibody for [Sjögren’s] patients in the future,” the researchers concluded.
About the Author
