Innate immunity in Sjögren's syndrome

Abstract

Sjögren's syndrome (SS) is an autoimmune disease of exocrine tissue that primarily affects women. Although patients typically experience xerostomia and xerophthalmia, numerous systemic disease manifestations are seen. Innate immune hyperactivity is integral to many autoimmune diseases, including SS. Results from SS mouse models suggest that innate immune dysregulation drives disease and this is a seminal event in SS pathogenesis. Findings in SS patients corroborate those in mouse models, as innate immune cells and pathways are dysregulated both in exocrine tissue and in peripheral blood. We will review the role of the innate immune system in SS pathogenesis. We will discuss the etiology of SS with an emphasis on innate immune dysfunction. Moreover, we will review the innate cells that mediate inflammation in SS, the pathways implicated in disease, and the potential mechanisms governing their dysregulation. Finally, we will discuss emerging therapeutic approaches to target dysregulated innate immune signaling in SS.

Keywords: A253; Innate immunity; Sjögren's syndrome; Submandibular gland; Toll-like receptor.

Figure 1. LPS activates TLR4 signaling in A253 cells

A253 cells were purchased from American Type Culture Collection. Cells were cultured in McCoy’s 5A (Modified) Media containing 10% heat-inactivated FBS, 2 mM L-glutamine, 100 U/mL penicillin, and 100 µg/mL streptomycin in 6 well plates. (A) A253 cells (3.5 × 10⁵) were harvested, and relative TLR4, Ly96, CD14, and MyD88 transcript levels were quantified by real time PCR. Each sample was analyzed in duplicate and normalized expression relative to GAPDH is shown. (B) A253 cells were harvested and cultured in the presence or absence of LPS (10 µg/mL) derived from Salmonella typhimurium for 24 h. Tissue was fluorescently stained with isotype control (grey shading) or TLR4 antibody. The red line represents unstimulated cells and the blue line indicates LPS treated cells. (C) A253 cells (3.0 × 10⁵) were incubated in the presence or absence LPS (10 µg/mL) for 24 h. Cells were lysed and western blots performed for MyD88. All samples were normalized to GAPDH. (D) A253 cells (3.0 × 10⁵) were stimulated with LPS (10 µg/mL) for the indicated times. Phosphorylated p65 was normalized to total p65 levels. Results of at least three independent experiments are shown (min = minutes).

Figure 2. LPS induces inflammatory cytokine secretion in A253 cells

A253 cells (3.0 × 10⁵) were cultured in the presence or absence of LPS (10 µg/mL) for 24 h, and the supernatant harvested. (A) IL-6, (B) IL-12, (C) MCP-1, (D) RANTES, and (E) GM-CSF were assessed by multiplex array. All samples were analyzed in triplicate and results of three independent experiments are shown (* p < 0.05, ** p < 0.001, *** p < 0.0001, N.S. = non significant).