Recently, the Th1/Th2 paradigm has been expanded by the discovery of Th17 cells, a subset of CD4+ memory T cells characterized by their unique ability to secrete interleukin-17 (IL-17) family cytokines. Importantly, Th17 cells appear to be intimately involved in autoimmunity. We undertook the present study to investigate whether the Th17/IL-23 system is up-regulated in Sjögren's syndrome (SS).
Sera, saliva, and salivary glands from C57BL/6.NOD-Aec1Aec2 mice (a model for primary SS), as well as sera, saliva, and salivary gland biopsy specimens obtained from patients with primary SS, were evaluated for IL-17 and IL-23 expression by immunohistochemistry, real-time polymerase chain reaction, and the Luminex system.
Immunohistochemical stainings of submandibular glands from C57BL/6.NOD-Aec1Aec2 mice and of salivary gland biopsy specimens from SS patients revealed strong positive staining for both IL-17 and IL-23 within lymphocytic foci and diffuse staining on epithelial tissues. Temporal expression of IL-17 and IL-23 in submandibular glands of C57BL/6.NOD-Aec1Aec2 mice correlated with expression of retinoic acid-related orphan receptor gammat, the Th17 cell master control gene. While IL-17 could not be detected in saliva from 4-20-week-old C57BL/6.NOD-Aec1Aec2 mice, this cytokine was present in the blood of mice up to age 16 weeks. This contrasted with sera and saliva from SS patients, in which IL-17 and IL-6 were present at varying levels.
These results suggest that the Th17/IL-23 system is up-regulated in C57BL/6.NOD-Aec1Aec2 mice and SS patients at the time of disease. A correlation between up-regulated IL-17/IL-23 expression and specific clinical manifestations of SS has yet to be identified.