Regulation of the polymeric Ig receptor by signaling through TLRs 3 and 4: linking innate and adaptive immune responses.
IgA Abs help to maintain homeostasis at mucosal surfaces by promoting defense mechanisms that protect against pathogens while suppressing inflammatory responses to commensal organisms and food Ags. The polymeric Ig receptor (pIgR) mediates transport of IgA across mucosal epithelial cells. We hypothesized that signaling through TLRs may up-regulate pIgR expression by intestinal epithelial cells and thus enhance IgA-mediated homeostasis. To test this hypothesis we treated the HT29 human intestinal epithelial cell line with dsRNA, a ligand for TLR3, or LPS, a ligand for TLR4. Both dsRNA and LPS up-regulated levels of pIgR mRNA and cell surface pIgR protein. By contrast, dsRNA but not LPS up-regulated expression of TLR3 and TLR4 mRNA. However, cell surface expression of both TLR3 and TLR4 was enhanced by treatment of HT29 cells with their respective ligands. Transfection of HT29 cells with wild-type and mutated promoter/enhancer plasmids suggested that TLR3 and TLR4 signal primarily through NF-kappaB to enhance transcription of pIgR mRNA. TLR3 signaling resulted in a more pronounced inflammatory response than did TLR4, as evidenced by up-regulation of the transcription factor IFN regulatory factor-1, chemokines IL-8 and RANTES, and the proinflammatory cytokine TNF. Signaling through LPS/TLR4 appears to up-regulate pIgR expression while minimizing proinflammatory responses, a mechanism that could promote IgA-mediated homeostasis in the presence of commensal Gram-negative bacteria.
Schneeman
Tracey A
TA
Department of Microbiology, Immunology and Molecular, University of Kentucky, Lexington, KY 40536, USA.
Bruno
Maria E C
ME
Schjerven
Hilde
H
Johansen
Finn-Eirik
FE
Chady
Laura
L
Kaetzel
Charlotte S
CS
D000222:Adaptation, Physiological; D001483:Base Sequence; D002460:Cell Line; D018946:Chemokine CCL5 / Q000096:biosynthesis; D004247:DNA / Q000235:genetics; D004268:DNA-Binding Proteins / Q000096:biosynthesis; D006801:Humans; D007113:Immunity, Innate; D066298:In Vitro Techniques; D018836:Inflammation Mediators / Q000378:metabolism; D050856:Interferon Regulatory Factor-1; D016209:Interleukin-8 / Q000096:biosynthesis; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D010750:Phosphoproteins / Q000096:biosynthesis; D012330:RNA, Double-Stranded / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D019056:Receptors, Polymeric Immunoglobulin / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D051196:Toll-Like Receptor 3; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis; D015854:Up-Regulation / Q000187:drug effects
D018946:Chemokine CCL5; D004268:DNA-Binding Proteins; C494257:IRF1 protein, human; D018836:Inflammation Mediators; D050856:Interferon Regulatory Factor-1; D016209:Interleukin-8; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D010750:Phosphoproteins; D012330:RNA, Double-Stranded; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D019056:Receptors, Polymeric Immunoglobulin; C495344:TLR3 protein, human; C495345:TLR4 protein, human; D051196:Toll-Like Receptor 3; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D014409:Tumor Necrosis Factor-alpha; D004247:DNA