Expression of type III interferons (IFNλs) and their receptor in Sjögren's syndrome

Abstract

Type III interferons (IFNs) or IFN-λs (IFN-λ1/IL29, IFN-λ2/interleukin (IL)-28A and IFN-λ3/IL-28B) consist of a recently identified group of IFNs, implicated initially in several human diseases, including cancer and autoimmunity. In this study, we sought to investigate the expression of type III IFNs and their common receptor IFN-λR1/IL-28Ra in Sjögren's syndrome (SS). Type III IFN expression was examined in minor salivary gland tissues (MSG), peripheral blood mononuclear cells (PBMCs), sera and resting or Toll-like receptor (TLR)-stimulated salivary gland epithelial cells (SGEC) from SS patients and sicca-complaining controls. All type III IFN family members were detected in ductal and acinar epithelia of MSGs from both SS patients and sicca controls. IFN-λ2/IL-28A and IFN-λ3/IL-28B were also expressed in infiltrating mononuclear cells. In SS patients with intermediate MSG lesions, the epithelial expression of IFN-λ2/IL-28A was more intense compared to sicca controls (P < 0·05). The receptor IFN-λR1/IL-28Ra was detected in all types of cells except fibroblasts, and was exceptionally strong in plasmatocytoid dendritic cells, indicating that they are susceptible to type III IFN-mediated regulation. In the periphery, only IFN-λ1/IL-29 was detected in the sera and was elevated significantly in SS patients with intermediate MSG inflammatory lesions compared to sicca controls (P = 0·0053). None of the type III IFNs was expressed constitutively in resting SGECs; they were all induced readily by TLR-3 stimulation, suggesting that the in-situ epithelial expression can be attributed to local microenvironment. Type III IFNs are expressed in MSGs in a similar pattern to type I IFNs and their expression is probably subjected to micro-environmental regulation, suggesting that they are implicated in the inflammatory processes occurring in the affected exocrine glands.

Keywords: TLRs; autoimmunity; cytokines; inflammation.

Figure 1

Expression of type III interferons (IFNs) (IFN‐λ1/interleukin (IL)−29, IFN‐λ2/IL‐28A and IFN‐λ3/IL‐28B) and their signalling receptor (IFN‐λR1/IL‐28Rα) (a) in minor salivary gland (MSG) tissues that belong to the three Sjögren's syndrome (SS) subgroups, as these classified by the grade of the inflammatory lesion (SS‐I: mild, n = 16; SS‐II: intermediate, n = 14; and SS‐III: severe, n = 16 MSG lesions. Sicca controls CT, n = 17), (b) in non‐malignant parotid glands of patients undergoing parotidectomy due to mixed tumours. Original magnification ×200.

Figure 2

Morphometric analysis of in‐situ interferon (IFN)‐λ2/interferon (IL)−28A‐positive signal per tissue area, per ductal area and respective stain intensity of positive signal in minor salivary glands (MSGs) of Sjögren's syndrome (SS) patients with mild (SS‐I), intermediate (SS‐II) and severe (SS‐III) MSG lesions and sicca controls (CT). Statistically significant differences are indicated.

Figure 3

Representative double immunofluorescent staining for the common type III interferon (IFN) signalling receptor [IFN‐λR1/interleukin (IL)−28Rα] and markers of inflammatory cells [plasmatocytoid dendritic cells (pDCs): CD303 and CD123, macrophages: CD68, T lymphocytes: CD3 and B lymphocytes: CD20] in a minor salivary gland (MSG) tissue from a Sjögren's syndrome (SS) patient. Co‐localization is indicated with yellow arrows. Original magnification ×1000.

Figure 4

(a) Detection of interferon (IFN)‐λ1/interleukin (IL)−29 in sera of healthy donors (HD), sicca controls (CT), total number of Sjögren's syndrome (SS) patients and SS patients classified by the grade of the inflammatory lesion [SS‐I: mild; SS‐II: intermediate and SS‐III: severe minor salivary gland (MSG) lesions]. Statistically significant differences are indicated. (b) Expression of IFN‐λ1/IL‐29 and IFN‐λ2/3‐IL‐28A/B mRNA in long‐term cultured salivary gland epithelial cells (SGECs) established from SS patients and non‐SS CTs following Toll‐like receptor (TLR)−3 ligation. Resting SGECs or treated with pI:C for various time‐points are shown. mRNA expression was assessed by quantitative real‐time polymerase chain reaction.