Selective roles for Toll-like receptor (TLR)2 and TLR4 in the regulation of neutrophil activation and life span.
Neutrophil responses to commercial LPS, a dual Toll-like receptor (TLR)2 and TLR4 activator, are regulated by TLR expression, but are amplified by contaminating monocytes in routine cell preparations. Therefore, we investigated the individual roles of TLR2 and TLR4 in highly purified, monocyte-depleted neutrophil preparations, using selective ligands (TLR2, Pam(3)CysSerLys(4) and Staphylococcus aureus peptidoglycan; TLR4, purified LPS). Activation of either TLR2 or TLR4 caused changes in adhesion molecule expression, respiratory burst (alone, and synergistically with fMLP), and IL-8 generation, which was, in part, dependent upon p38 mitogen-activated protein kinase signaling. Neutrophils also responded to Pam(3)CysSerLys(4) and purified LPS with down-regulation of the chemokine receptor CXCR2 and, to a lesser extent, down-regulation of CXCR1. TLR4 was the principal regulator of neutrophil survival, and TLR2 signals showed relatively less efficacy in preventing constitutive apoptosis over short time courses. TLR4-mediated neutrophil survival depended upon signaling via NF-kappa B and mitogen-activated protein kinase cascades. Prolonged neutrophil survival required both TLR4 activation and the presence of monocytes. TLR4 activation of monocytes was associated with the release of neutrophil survival factors, which was not evident with TLR2 activation, and TLR2 activation in monocyte/neutrophil cocultures did not prevent late neutrophil apoptosis. Thus, TLRs are important regulators of neutrophil activation and survival, with distinct and separate roles for TLR2 and TLR4 in neutrophil responses. TLR4 signaling presents itself as a pharmacological target that may allow therapeutic modulation of neutrophil survival by direct and indirect mechanisms at sites of inflammation.
Academic Unit of Respiratory Medicine, Section of Functional Genomics, Division of Genomic Medicine, University of Sheffield, Sheffield, United Kingdom.
Ian
I
Sabroe
Lynne R
LR
Prince
Elizabeth C
EC
Jones
Malcolm J
MJ
Horsburgh
Simon J
SJ
Foster
Stefanie N
SN
Vogel
Steven K
SK
Dower
Moira K B
MK
Whyte
D015815:Cell Adhesion Molecules / Q000096:biosynthesis; D002450:Cell Communication / Q000502:physiology; D002469:Cell Separation; D002470:Cell Survival / Q000502:physiology; D015536:Down-Regulation / Q000502:physiology; D004357:Drug Synergism; D006801:Humans; D016209:Interleukin-8 / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000378:metabolism / Q000502:physiology*; D009000:Monocytes / Q000502:physiology; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D018375:Neutrophil Activation / Q000502:physiology*; D009504:Neutrophils / Q000166:cytology* / Q000378:metabolism / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000378:metabolism / Q000502:physiology*; D019707:Receptors, Chemokine / Q000096:biosynthesis; D016897:Respiratory Burst / Q000187:drug effects / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D015854:Up-Regulation / Q000502:physiology
D015815:Cell Adhesion Molecules; D016209:Interleukin-8; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D011956:Receptors, Cell Surface; D019707:Receptors, Chemokine; C495342:TLR2 protein, human; C495345:TLR4 protein, human; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D009240:N-Formylmethionine Leucyl-Phenylalanine