DNA microarray analysis of labial salivary glands in IgG4-related disease – comparison with Sjögren’s syndrome

To compare gene expression in labial salivary glands (LSG) of IgG4-related disease (IgG4-RD) with Sjögren’s syndrome (SS). Gene expression was analyzed by DNA microarray in LSG of IgG4-RD (n=5), SS (n=5), and healthy controls (n=3). Differentially expressed genes (DEGs) in IgG4-RD and SS were identified, and gene-annotation enrichment analysis of these DEGs was performed using Gene Ontology (GO) annotation. Validation of the result was performed by quantitative PCR using LSG from IgG4-RD (n=9), SS (n=10), and controls (n=4). Gene expression patterns in IgG4-RD, SS, and healthy controls were quite different with each other in hierarchical clustering as well as principal component analysis. In IgG4-RD, 1771 up-regulated probe sets (corresponding to 1321 up-regulated genes) and 1785 down-regulated probe sets (corresponding to 1320 down-regulated genes) were identified as DEGs (false discovery rate <0.05). GO term analysis indicated that the up-regulated set of DEGs in IgG4-RD encoded proteins that function in cell proliferation, extracellular matrix organization, and organ development. PCR validated significantly higher expression of lactotransferrin (LTF) in IgG4-RD than SS (P<0.05), and chemokine (C-C motif) ligand 18 (CCL18) in IgG4-RD than SS and controls (P<0.05). The results clearly showed that the gene expression pattern in LSG of IgG4-RD is different from that of SS. LSG samples were collected from 5 Japanese patients with IgG4-RD, as well as from 5 Japanese patients with SS who had been followed up at University of Tsukuba Hospital (Ibaraki, Japan). All patients with IgG4-RD satisfied the comprehensive diagnostic criteria for IgG4-related disease (IgG4-RD) 2011 proposed by the All Japan IgG4 team [3]. The diagnosis of IgG4-RD was based on the presence of all three items; 1) clinical examination showing characteristic diffuse/localized swelling or masses in single or multiple organs, 2) Hematological examination shows elevated serum IgG4 concentrations (135 mg/dl), 3) Histopathologic examination shows: (1) Marked lymphocyte and plasmacyte infiltration and fibrosis. (2) Infiltration of IgG4+ plasma cells: ratio of IgG4+/IgG+ cells > 40% and >10 IgG4+ plasma cells/HPF. All patients with SS satisfied the Japanese Ministry of Health criteria for the diagnosis of SS (1999) [4]. These criteria included four clinicopathological findings: lymphocytic infiltration of the salivary or lacrimal glands, dysfunction of salivary secretion, keratoconjunctivitis sicca, and presence of anti-SS-A or SS-B antibodies. The diagnosis of SS was based on the presence of two or more of the above four items. Approval for this study was obtained from the local ethics committee and a signed informed consent was obtained from each subject.