The Proteomic Characteristics Of Saliva And The Application Value Of PET-CT In IgG4-related Disease

ObjectiveIgG4-related disease is a chronic inflammation mediated autoimmune disease,which involves multiple organs(such as lacrimal glands,salivary glands,sinuses,lymph nodes,pancreas,bile ducts,retroperitoneal,mediastinum,lungs,kidneys,prostate,etc.),characterized by significantly increased serum IgG4 levels,enlargement of involved organs,and infiltration of IgG4-positive plasma cells.Although significant progress has been made in the diagnosis of IgG4-RD in recent years,due to the heterogeneity of the clinical manifestations of IgG4-RD,the diversity of differential diagnoses,and the high dependence of IgG4-RD diagnosis on biopsy of the affected organ,biopsy specimens are not always readily available in clinical practice.There are certain challenges in diagnosis.Therefore,exploring the biological characteristics of different subtypes of IgG4-RD and discovering noninvasive imaging information on the overall disease distribution of the system is critical for the diagnosis and treatment of IgG4-RD.The objective of this study is to explore the characteristics of expressed proteins in the saliva of IgG4-RD patients through proteomics technology,to gain insight into the differences in protein levels between diverse clinical phenotypes of IgG4-RD,to provide biomarkers for the classification and diagnosis of IgG4-RD,and may play a role in further subclassification and prognosis of IgG4-RD in the future.At the same time,we also explore the clinical application value of 18F-deoxyglucose positron emission tomography/computed tomography(18F-FDG PET/CT)in IgG4-RD by analyzing the relation between 18F-FDG PET/CT and IgG4-RD histopathology and its role in clinical diagnostic criteria.MethodsWe performed proteomic analysis realized with i TRAQ technology for saliva samples from ten untreated IgG4-RD patients and five sex-and age-matched healthy controls.Differentially expressed proteins(DEPs)were identified by ‘t test’ function in R package(version 3.6).Functional enrichment analysis was used to investigate pathways enriched in IgG4-RD samples.To explore the role of PET.CT in IgG4-RD,72 patients diagnosed with IgG4-RD who underwent PET/CT were included.Correlations between clinical variables and PET/CT findings were analyzed by Spearman’s correlation test.Conventional radiology was compared to PET/CT to evaluate detection discrepancies.The detection ability of insidious organ involvement by PET/CT at disease onset was investigated.The utility value of PET/CT for the 2019 ACR/EULAR classification criteria was analyzed with the multivariate logistic analysis and ROC curve.Results1.A total of 64 differentially expressed proteins were identified in the saliva of IgG4-RD patients compared with HCs,and most DEPs were enriched in neutrophil mediated GO bioprocess.PARK7 expression was positively correlated with Ig G,Ig G1,and IgG4 levels,while CST4 expression was negatively correlated with Ig G,Ig G1,and IgG4 levels.Within the four IgG4-RD subgroups,there were much more DEPs identified in the comparisons of Mikulicz group/ Retroperitoneal aorta group versus Head and neck group than in other comparisons and “Neutrophil mediated process” related GO bioprocess category was common and FCN1,MPO and HK3 are all involved.In addition,“Fc gamma-mediated phagocytosis” process was significantly enriched in Mikulicz group compared with Head and neck group/ Retroperitoneal fibrosis group and increased IGLV2-11 and IGLV7-43 were both involved in this pathway.In terms of the comparisons between IgG4-RD patients with four distinctive phenotypes and HCs,results showed that more DEPs were identified in the comparison between Head and neck group/ Retroperitoneal aorta group and HC and “neutrophil mediated related GO BP categories” were common.In the comparison between IgG4-RD patients with and without saliva gland involvement,functional enrichment analysis also showed that DEPs were mainly enriched in “Neutrophil mediated related GO BP categories”.Elevation of SLPI expression was positively correlated with IgG4 level,while decreasing of HSPA8 expression was negatively correlated with Ig G2 level.In this study,we also collected plasma samples of ten IgG4-RD and five HC for analysis.There are more DEPs detected in plasma than in saliva.Meanwhile,we found nine DEPs overlapped in saliva and plasma,and LGALS3,a protein involved in platelet degranulation,was found increased in saliva of IgG4-RD patients.2.SUVmax of main involved organ was positively correlated with IgG4-RD Responder Index(IgG4-RD RI),serum and tissue IgG4 levels and IgG4/Ig G ratio,serum eosinophils counts and number of involved organs,while negatively correlated with serum Ig M levels.PET/CT was superior in detecting organ/tissue involvements including prostate,gastrointestinal tract and lung compared with conventional imaging.For patients with pancreato-hepato-biliary or head-neck involvements at onset,PET/CT showed superiority in detecting insidious lesions.Multivariate analysis showed that disease duration,multiple-organ involvement,SUVmax of main involved organ and mean SUVmax of all involved organs were significantly associated with the fulfillment of the 2019 ACR/EULAR classification criteria.ROC curves indicated that the cut-off value for SUVmax of main involved organ and mean SUVmax of all involved organs for fulfillment of the 2019 ACR/EULAR classification criteria for IgG4-RD were 4.1 and 3.5,respectively.ConclusionsWe identified multiple processes/factors and several signaling pathways in saliva that may be involved in the IgG4-RD pathogenesis.Besides,18F-FDG PET/CT has potential capacity to monitor disease activity,evaluate organ involvements and assist in the classification criteria in IgG4-RD.