[Diagnostic values of anti-salivary gland protein-1 antibody combined with anti-parotid secretory protein antibody for Sjögren's syndrome].

Objective: To assess the diagnostic value of anti-salivary gland protein-1 (SP1) antibody combined with anti-parotid secretory protein (PSP) antibody for Sjögren's syndrome (SS).

Methods: A total of 60 patients with primary SS (pSS) who were treated in the outpatient and inpatient department of Department of Rheumatology and Immunology of the Second Hospital of Hebei Medical University from January 2020 to December 2022 were collected. Thirty patients with other autoimmune diseases accompanied by dry mouth and/or dry eyes were collected as disease control group. Thirty healthy subjects from the physical examination center were collected for healthy control group, serum samples were obtained from all of them. Their general features and clinical information including clinical manifestations, laboratory examinations and other examinations were recorded. The 2016 American College of Rheumatology (ACR)/European League against Rheumatism (EULAR) classification criteria were adopted as the diagnostic standard of pSS. Immunoglobulin G (IgG) subtype of anti-SP1 antibody and anti-PSP antibody were detected by chemiluminescence immunoassay. The receiver operating characteristic (ROC) curve was used to evaluate the accuracy of anti-SP1 antibody and anti-PSP antibody in diagnosing pSS.The cli-nical characteristics of anti-SP1 antibody and anti-PSP antibody positive patients and negative patients in pSS group were further compared. Independent samples t test, Mann-Whitney U test, variance analysis, Kruskal-Wallis test, Chi-square test or Fisher's exact test and Spearman correlation analysis were used for statistical analysis.

Results: There was no significant difference in age (F=1.406, P=0.495) and gender (χ²=2.105, P=0.349) among pSS group, disease control group and healthy control group. The expression levels of anti-SP1 antibody (H=16.73, P < 0.001) and anti-PSP antibody (H=26.09, P < 0.001) were statistically different among the three groups. An intergroup comparison of anti-SP1 antibody expression levels showed that there was a statistically significant difference between pSS and healthy control group (P < 0.001), but no statistically significant difference between the other groups. Comparison of anti-PSP antibody expression levels between the groups showed that there were statistically significant differences between pSS and healthy control group (P < 0.001), and between disease control group and healthy control group (P=0.009), while no statistically significant differences between the other groups. The positive rate of anti-SP1 antibody in pSS group was significantly higher than that in disease control group and healthy control group (58.33% vs. 40.00% vs. 13.33%, P < 0.001). The positive rate of anti-PSP antibody in pSS group was significantly higher than that in disease control group and healthy control group (75.00% vs. 56.17% vs. 16.67%, P < 0.001). The area under the curve for anti-SP1 antibody was 0.688 (P < 0.001). The sensitivity and specificity of anti-SP1 antibody were 58.33% (35/60) and 70.00% (42/60) respectively, the positive predictive value was 66.04% (35/53) and the negative predictive value was 54.55% (42/77) of anti-SP1 antibody.The area under the curve of anti-PSP antibody was 0.720 (P < 0.001), with a sensitivity was 75.00% (45/60), and specificity was 63.33% (38/60).The positive predictive value and negative predictive value of anti-PSP antibody were 67.16% (45/67) and 71.70% (38/53) respectively. All the 13 pSS patients were negative for anti-Sjögren's syndrome A (SSA, including SSA52 and SSA60) antibody and anti- Sjögren's syndrome B (SSB) antibody. Among them, 11 patients were positive for both anti-SP1 antibody and anti-PSP antibody, 1 patient was positive for anti-SP1 antibody and 1 patient was positive for anti-PSP antibody. The clinical features of anti-SP1 antibody and anti-PSP antibody positive and negative groups were compared in pSS patients. The duration of disease in anti-SP1 antibody positive group was shorter (Z=-2.277, P=0.023) when compared with the negative patients. The patients with positive anti-PSP antibody were younger than those in the negative group (t=2.598, P < 0.05), the positive rate of rheumatoid factor (P=0.002) and the serum level of IgG (t=3.806, P=0.003) in anti-PSP antibody positive group were higher than in the negative group. Analysis of the correlation between anti-SP1 antibody and anti-PSP antibody in the pSS patients showed that there was significant correlation between them (r=0.801, P < 0.001).

Conclusion: Both anti-SP1 antibody and anti-PSP antibody are valuable in the diagnosis of SS, and anti-SP1 antibody is helpful for the early diagnosis of pSS. The combined detection of anti-SP1 antibody and anti-PSP antibody is helpful for the early diagnosis of pSS patients with negative anti-SSA antibody and anti-SSB antibody.