Innate immune responses to Mycobacterium ulcerans via toll-like receptors and dectin-1 in human keratinocytes.
Mycobacterium ulcerans (MU), an environmental pathogen, causes Buruli ulcer, a severe skin disease. We hypothesized that epidermal keratinocytes might not be a simple barrier, but play a role during MU infection through pattern-recognition receptors expressed in keratinocytes. We found that keratinocyte Toll-like receptors (TLRs) 2 and 4 and Dectin-1 actively participate in the innate immune response to MU, which includes the internalization of bacteria, the production of reactive oxygen species (ROS), and the expression of chemokines and LL-37. Human keratinocytes constitutively expressed TLRs 2 and 4 and induced Dectin-1 in response to MU. Exposing keratinocytes to MU resulted in rapid ROS production, which in turn contributed to the mRNA and protein expression of LL-37. In addition, TLR2, Dectin-1 and, to an extent, TLR4 are essential for the MU-mediated expression of CXCL8, CCL2 and LL-37 in keratinocytes. Furthermore, confocal analysis showed that the Dectin-1 is necessary for keratinocytes to internalize bacilli. Importantly, blockade of ROS and LL-37 significantly increased the intracellular MU growth in keratinocytes, suggesting an important role of these mediators for cutaneous innate immune responses. Our results demonstrate that TLR2, TLR4 and Dectin-1 actively sense, internalize and respond in an innate way to MU in human epidermal keratinocytes.
Lee
Hye-Mi
HM
Department of Microbiology, Chungnam National University, Daejeon, South Korea.
Shin
Dong-Min
DM
Choi
Dae-Kyoung
DK
Lee
Zee-Won
ZW
Kim
Ki-Hye
KH
Yuk
Jae-Min
JM
Kim
Chang Deok
CD
Lee
Jeung-Hoon
JH
Jo
Eun-Kyeong
EK
D023181:Antimicrobial Cationic Peptides / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D002478:Cells, Cultured; D018925:Chemokines / Q000235:genetics / Q000378:metabolism; D000078404:Epidermal Cells; D004817:Epidermis / Q000276:immunology / Q000382:microbiology; D005786:Gene Expression Regulation / Q000276:immunology; D054884:Host-Pathogen Interactions; D006801:Humans; D007113:Immunity, Innate; D015603:Keratinocytes / Q000276:immunology / Q000378:metabolism / Q000382:microbiology; D037181:Lectins, C-Type; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D019911:Mycobacterium ulcerans / Q000276:immunology / Q000472:pathogenicity*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D051195:Toll-Like Receptor 2 / Q000235:genetics / Q000378:metabolism*; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism*; D054804:Cathelicidins; D000099181:Dectin-1
D023181:Antimicrobial Cationic Peptides; D018925:Chemokines; D037181:Lectins, C-Type; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D054804:Cathelicidins; D000099181:Dectin-1; C495342:TLR2 protein, human