Profiling Autoantibodies against Salivary Proteins in Sicca Conditions

Abstract

Salivary gland dysfunction occurs in several autoimmune and immune-related conditions, including Sjögren syndrome (SS); immune checkpoint inhibitor-induced sicca (ICIS) that develops in some cancer patients and is characterized by severe, sudden-onset dry mouth; and autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED). Although subjects with these conditions present with oral dryness and often exhibit inflammatory infiltration of the salivary gland, little is known about the B-cell humoral responses directed against salivary gland protein targets. In this study, autoantibodies were evaluated against Ro52, Ro60, and La, as well as against a panel of 22 proteins derived from the salivary proteome. The tested cohort included healthy volunteers and subjects with SS, ICIS, and APECED without and with sicca. As expected, a high percentage of autoantibody seropositivity was detected against Ro52, Ro60, and La in SS, but only a few ICIS patients were seropositive for these autoantigens. A few APECED subjects also harbored autoantibodies to Ro52 and La, but only Ro60 autoantibodies were weakly associated with a small subset of APECED patients with sicca. Additional testing of the salivary panel failed to detect seropositive autoantibodies against any of the salivary-enriched proteins in the SS and ICIS subjects. However, APECED subjects selectively demonstrated seropositivity against BPI fold containing family A member 1 (BPIFA1), BPI fold containing family A member 2 (BPIFA2)/parotid salivary protein (PSP), and lactoperoxidase, 3 salivary-enriched proteins. Moreover, high levels of serum autoantibodies against BPIFA1 and BPIFA2/PSP occurred in 30% and 67% of the APECED patients with sicca symptoms, respectively, and were associated with an earlier age onset of oral dryness (P = 0.001). These findings highlight the complexity of humoral responses in different sicca diseases and provide new insights and biomarkers for APECED-associated sicca (ClinicalTrials.gov: NCT00001196; NCT00001390; NCT01425892; NCT01386437).

Keywords: Sjögren syndrome (SS); autoimmune; autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED); immune check-point inhibitor treated cancer patients with sicca (ICIS); saliva; salivary gland.

Conflict of interest statement

The authors declare no potential conflicts of interest with respect to the authorship and/or publication of this article.<?release-delay 12|0>

Figures

Figure 1.

Serum autoantibodies against Ro52, Ro60, and La in the sicca cohort. Scatterplot graphs represent autoantibody levels determined by luciferase immunoprecipitation systems (LIPS) in subjects from the cohort of healthy volunteers (HVs, n = 20), subjects with Sjögren syndrome (SS) (n = 20), subjects with immune checkpoint inhibitor-induced sicca (ICIS) (n = 23), and autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) subjects without sicca (n = 11, open circles) and with sicca (n = 9, black circles). Autoantibodies were studied against (A) Ro52, (B) Ro60, and (C) La. Each circle represents antibody levels in light units (LU) derived from subjects plotted on the y-axis using a log10 scale. Seropositive cutoff values for each autoantibody are indicated with a dotted line and were based on the mean plus 5 SD of the HV control group. Only statistically significant P values are shown and were calculated using the Mann-Whitney U test.

Figure 2.

Identification of autoantibodies against salivary-enriched proteins in autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) subjects. Scatterplot graphs represent autoantibody levels determined by luciferase immunoprecipitation systems (LIPS) in subjects from the cohort of healthy volunteers (HVs) and patients with Sjögren syndrome (SS), immune checkpoint inhibitor-induced sicca (ICIS), and APECED without sicca (open circles) and with sicca (black circles). Autoantibodies against salivary proteins are shown against (A) lactoperoxidase (LPO), (B) BPI fold containing family A member 2 (BPIFA2), and (C) BPI fold containing family A member 1 (BPIFA1). Cutoff antibody levels for each salivary protein are indicated with a dotted line and were based on the mean plus 5 SD of the HV control group. Additional cutoff values (gray dashed line) for BPIFA1 and BPIFA2 were based on receiver operator characteristic curve analysis for optimum separation of the APECED patients with and without sicca. (D) Autoantibodies against LPO, BPIFA1, and BPIFA2 were also examined in whole saliva from available APECED subjects (n = 16). BPIFA1 autoantibodies were present in saliva in 2 subjects, which tracked the corresponding values seen in serum (1 low BPIFA2-seropositive subject had no available saliva). LU, light units.

Figure 3.

BPI fold containing family A member 2 (BPIFA2) and BPI fold containing family A member 1 (BPIFA1) autoantibodies associate with the development of sicca in younger autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) subjects. Kaplan-Meier estimator was used to examine the relationship between the 3 salivary autoantibodies and time until development of sicca in the APECED patients. Subjects were segregated based on presence and absence of autoantibodies against (A) lactoperoxidase (LPO), (B) BPIFA2, and (C) BPIFA1 and plotted against age of sicca onset. The gray and black bars at the top of graph curves indicate additional APECED subjects who were autoantibody negative or positive and had not developed sicca. Log rank (Mantel-Cox) tests were used to confirm statistical significance of the findings.