title: The MyD88-independent pathway is not mobilized in human neutrophils stimulated via TLR4.
abstract: LPS activates both MyD88-dependent and -independent signaling via TLR4, but the extent to which each cascade is operative in different cell types remains unclear. This prompted us to revisit the intriguing issue of CXCL10 production, which we previously showed to be inducible in neutrophils stimulated with LPS and IFN-gamma but not with either stimulus alone, contrary to other myeloid cells. We now report that in neutrophils the MyD88-independent pathway is not activated by LPS. Indeed, microarray and real-time PCR experiments showed that neither IFNbeta nor IFNbeta-dependent genes (including CXCL10) are inducible in LPS-treated neutrophils, in contrast to monocytes. Further investigation into the inability of LPS to promote IFNbeta expression in neutrophils revealed that the transcription factors regulating the IFNbeta enhanceosome, such as IFN-regulatory factor-3 and AP-1, are not activated in LPS-treated neutrophils as revealed by lack of dimerization, nuclear translocation, confocal microscopy, and inducible binding to DNA. Moreover, we show that the upstream TANK-binding kinase-1 is not activated by LPS in neutrophils. A lack of IFNbeta/CXCL10 mRNA expression and IFN-regulatory factor 3 activation was also observed in myeloid leukemia HL60 cells differentiated to granulocytes and then stimulated with LPS, indicating that the inability of neutrophils to activate the MyD88-independent pathway represents a feature of their terminal maturation. These results identify a disconnected activation of the two signaling pathways downstream of TLR4 in key cellular components of the inflammatory and immune responses and help us to better understand the primordial role of neutrophils in host defense against nonviral infections.
authors.affiliation: Department of Pathology, University of Verona, Verona, Italy.
authors.forename: Nicola
authors.initials: N
authors.lastname: Tamassia
authors.forename: Vincent
authors.initials: V
authors.lastname: Le Moigne
authors.forename: Federica
authors.initials: F
authors.lastname: Calzetti
authors.forename: Marta
authors.initials: M
authors.lastname: Donini
authors.forename: Sara
authors.initials: S
authors.lastname: Gasperini
authors.forename: Thornin
authors.initials: T
authors.lastname: Ear
authors.forename: Alexandre
authors.initials: A
authors.lastname: Cloutier
authors.forename: Fernando O
authors.initials: FO
authors.lastname: Martinez
authors.forename: Marco
authors.initials: M
authors.lastname: Fabbri
authors.forename: Massimo
authors.initials: M
authors.lastname: Locati
authors.forename: Alberto
authors.initials: A
authors.lastname: Mantovani
authors.forename: Patrick P
authors.initials: PP
authors.lastname: McDonald
authors.forename: Marco A
authors.initials: MA
authors.lastname: Cassatella
mesh_terms: D002454:Cell Differentiation / Q000276:immunology; D002460:Cell Line; D002478:Cells, Cultured; D054357:Chemokine CXCL10; D019743:Chemokines, CXC / Q000096:biosynthesis / Q000235:genetics; D005786:Gene Expression Regulation / Q000276:immunology; D018922:HL-60 Cells; D006801:Humans; D016899:Interferon-beta / Q000502:physiology; D008070:Lipopolysaccharides / Q000302:isolation & purification / Q000494:pharmacology; D009000:Monocytes / Q000276:immunology / Q000378:metabolism; D053594:Myeloid Differentiation Factor 88 / Q000378:metabolism / Q000502:physiology*; D018375:Neutrophil Activation / Q000235:genetics / Q000276:immunology; D009504:Neutrophils / Q000166:cytology / Q000276:immunology* / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology*; D051197:Toll-Like Receptor 4 / Q000502:physiology*
chemical_list: D054357:Chemokine CXCL10; D019743:Chemokines, CXC; D008070:Lipopolysaccharides; C507779:MYD88 protein, human; D053594:Myeloid Differentiation Factor 88; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D016899:Interferon-beta