We investigated expression of toll-like receptor (TLR) in labial salivary glands of patients with Sjögren's syndrome (SS) and functional TLR expression in the cultured salivary gland cell line.
Expression of TLR2, TLR3, TLR4, and myeloid differentiation factor 88 (MyD88) in labial salivary glands was examined by immunohistochemistry. Human salivary gland (HSG) cell-line cells were cultured with TLR ligands [peptidoglycan, poly (I:C) and lipopolysaccharide], and CD54 expression and interleukin 6 (IL-6) production was studied. Phosphorylation of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), p38, and Akt was examined by Western blotting. Activation of nuclear factor-kappaB (NF-kappaB) p65 in HSG cells was studied by NF-kappaB p65 nuclear translocation by microscopic immunofluorescence or chemiluminescent electrophoretic mobility shift assay and detection of NF-kappaB p65 phosphorylation.
TLR2, TLR3, TLR4, and MyD88 were more strongly expressed in the labial salivary glands of SS patients (n =12) than in control subjects (n = 4), and were found in salivary-infiltrating mononuclear cells as well as acinar cells and ductal epithelial cells. In cultured HSG cells, a similar expression pattern was observed, and TLR ligands stimulated CD54 expression and IL-6 production. TLR ligands induced phosphorylation of ERK, JNK, and p38 in HSG cells, but not Akt phosphorylation or activation of NF-kappaB p65.
Although the putative ligands remain to be determined, our study indicated the activation of the TLR-mediated immune response in SS, and suggested that the TLR effect is mediated through the mitogen-activated protein kinase pathway.