Sjögren's syndrome (SS) is a chronic autoimmune disease characterised by dry eyes, dry mouth and focal lymphocytic infiltration in lacrimal and salivary glands. The infiltrating lymphocytes are mainly CD4 α/β T cells,1 especially T helper 1 (Th1) type T cells, because they produce both interferon (IFN)γ and interleukin 2.2,3 To understand the pathogenesis of SS, several molecules in labial salivary glands (LSGs) have been screened by microarray analysis in human SS. Hjelmervik et al4 and Gottenberg et al5 reported that the upregulated genes in SS salivary glands were IFN‐inducible genes, such as IFN‐stimulated transcription factor 3, IFN‐regulatory factor 1 and B cell‐activation factor of the TNF family. However, there is little or no information on the essential genes involved in the generation of sialoadenitis in patients with SS. We screened abnormally expressed genes in LSGs of patients with SS using cDNA microarray technology to elucidate the SS susceptibility genes.
The cDNA array was performed using total RNA from LSGs of three patients with primary SS and from three healthy subjects (control) with a DNA chip including 775 genes (JGS, Tokyo, Japan). The DNA chip contained immunoglobulins, human leucocyte antigens (HLAs), complements, T cell receptors (TCRs), IFN‐inducible proteins, cytokines, transcriptional factors and other autoimmune disease‐related genes. Abnormally expressed genes in SS LSG represented those with expression level over twofold or below 0.5‐fold of that of LSGs of the controls. The Mann–Whitney U test was used for statistical analysis. p Values <0.05 were considered significant.
A total of 24 upregulated genes were identified in LSGs (table 1). These included immunoglobulins, HLAs, complements, TCRs, IFN‐inducible proteins, thymosin β and transcriptional factors. We also identified one single downregulated gene, LIM protein. Among the abnormally expressed genes in SS LSG, expression level 19 was significantly higher than in the controls. These included thymosin β4 and thymosin β10, the regulators of apoptosis activity and inflammation‐related genes such as HLA‐DR and TCRβ. Upregulation of HLA, complements, TCRs and immunoglobulins should be due to the infiltration of T cells and B cells in LSGs from patients with SS. Interestingly, many IFNγ‐inducible genes, such as IP10, STAT1α and STAT1β, were highly expressed in SS, and our previous study reported that STAT1 could function as a key molecule in the pathogenesis of SS.6 These findings suggest that Th1 cells and Th1 type cytokines function as destructive factors in the generation of sialoadenitis in LSGs of patients with SS. Thymosin β has anti‐apoptotic activity,7 suggesting that it may function as a protective factor against salivary gland destruction in patients with SS.
Table1 Genes expressed in labial salivary glands of patients with Sjögren's syndrome (SS).
| Gene name | SS/HS |
|---|---|
| Upregulated genes | |
| Immunoglobulin (Ig) | |
| Ig heavy constant γ3 | 8.40* |
| Igγ chain; Ig rearranged γ chain, V‐J‐C region | 2.99 |
| Ig κ variable 1D8 | 3.25 |
| Rearranged Ig mRNA for μ heavy chain enhancer and constant region | 2.23 |
| Human leucocyte antigen (HLA) | |
| Human MHC HLA class I cell surface antigen (HLA‐B 5102) mRNA | 6.56* |
| HLA‐F | 3.31* |
| HLA‐DRβ1 | 6.22* |
| HLA‐DP light chain | 3.01* |
| RING6 (HLA class II α chain‐like product) | 2.41* |
| MHC class II DQ | 2.35* |
| MHC class II DR | 7.28* |
| Complement | |
| Complement C3 | 3.96* |
| T cell receptor (TCR) | |
| TCRβ chain (T cell receptor β chain) | 2.11* |
| Interferon (IFN)‐inducible genes | |
| IP‐30 (IFNγ‐inducible protein) | 2.17* |
| I‐5111 (IFNγ‐inducible gene) | 2.25 |
| IP‐10 (IFNγ‐inducible chemokine) | 2.31 |
| IFNα/β‐inducible p44 | 2.1* |
| IFN‐α‐inducible protein 27 | 2.19* |
| Staf50 mRNA | 2.04* |
| Thymosin β | |
| Thymosin β4 | 2.03* |
| Thymosin β10 | 2.12* |
| Transcription factor | |
| STAT1α | 2.88* |
| STAT1β | 2.07* |
| I κ B | 2.02* |
| Downregulated genes | |
| LIM protein (cystein‐rich protein 3) | 0.44 |
MHC, major histocompatibility complex.
The average of patients with SS healthy subjects based on cDNA array fluorescent data healthy subjects (n = 3, each). The Mann–Whitney U test was used to compare the control and SS groups.
*p<0.05.
Recent studies reported the presence of germinal centre‐like structures in the salivary glands of patients with SS, and that the germinal centre formed by infiltrating mononuclear cells (B cells, T cells and others) produces autoantibodies and exhibits apoptosis.8,9 In this study, the significant upregulation of 10 genes—for example, IgHCγ, HLA class l, HLA class ll, C3 and TCRβ—might be due to mononuclear infiltrates and might be responsible for the formation of a germinal centre, in LSGs of patients with SS.
In conclusion, cDNA microarray analysis demonstrated upregulation of IFNγ‐related genes in LSGs of patients with SS, indicating that Th1 cells might play a crucial role in the generation of sialoadenitis in those patients.
Abbreviations
HLA - human leucocyte antigen
SS - Sjögren's syndrome
IFN - interferon
LSG - labial salivary gland Th1, T helper cell
TCR - T cell receptor
Footnotes
Competing interests: None declared.
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