Intracellularly expressed TLR2s and TLR4s contribution to an immunosilent environment at the ocular mucosal epithelium.
Epithelial cells are key players in the first line of defense offered by the mucosal immune system against invading pathogens. In the present study we sought to determine whether human corneal epithelial cells expressing Toll-like receptors (TLRs) function as pattern-recognition receptors in the innate immune system and, if so, whether these TLRs act as a first line of defense in ocular mucosal immunity. Incubation of human primary corneal epithelial cells and the human corneal epithelial cell line (HCE-T) with peptidoglycan or LPS did not lead to activation, at the level of DNA transcription, of NF-kappaB or the secretion of inflammation-associated molecules such as IL-6, IL-8, and human beta-defensin-2. However, when incubated with IL-1alpha to activate NF-kappaB, the production by these cells of such inflammatory mediators was enhanced. Human corneal epithelial cells were observed to express both TLR2- and TLR4-specific mRNA as well as their corresponding proteins intracellularly, but not at the cell surface. However, even when LPS was artificially introduced into the cytoplasm, it did not lead to the activation of epithelial cells. Taken together, our results demonstrate that the intracellular expression of TLR2 and TLR4 in human corneal epithelial cells fails to elicit innate immune responses and therefore, perhaps purposely, contributes to an immunosilent environment at the ocular mucosal epithelium.
Department of Mucosal Immunology, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan.
Mayumi
M
Ueta
Tomonori
T
Nochi
Myoung-Ho
MH
Jang
Eun Jeong
EJ
Park
Osamu
O
Igarashi
Ayako
A
Hino
Satoshi
S
Kawasaki
Takashi
T
Shikina
Takachika
T
Hiroi
Shigeru
S
Kinoshita
Hiroshi
H
Kiyono
D003315:Cornea / Q000276:immunology* / Q000378:metabolism; D004848:Epithelium / Q000276:immunology / Q000378:metabolism; D006801:Humans; D007108:Immune Tolerance / Q000276:immunology* / Q000502:physiology; D007150:Immunohistochemistry; D008070:Lipopolysaccharides / Q000276:immunology; D008562:Membrane Glycoproteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D009092:Mucous Membrane / Q000276:immunology / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors
D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; C495342:TLR2 protein, human; C495345:TLR4 protein, human; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors