Intracellular signaling mechanisms regulating toll-like receptor-mediated activation of eosinophils.
Activation of eosinophils by microbe-derived molecules via Toll-like receptors (TLR) potentially provides the link between microbe-induced innate immune responses and the exacerbation of allergic inflammation. We investigated the expression of TLRs and the effect of their ligands on human eosinophils. Expression of TLR1-9 was detected by Western blot and flow cytometry. Adhesion molecules, cytokines, superoxides, and eosinophlilic cationic protein (ECP) were assessed by flow cytometry, enzyme-linked immunosorbent assay, chemiluminescent method, and fluorescence immunoassay, respectively. Human eosinophils differentially expressed TLR1, -2, -4, -5, -6, -7, and -9. Peptidoglycan (PGN) (TLR2 ligand), flagellin (TLR5 ligand), and Imiquimod R837 (TLR7 ligand) could significantly upregulate cell surface expression of intercellular adhesion molecule (ICAM)-1 and CD18, and induce the release of IL-1beta, IL-6, IL-8, growth-related oncogene (GRO)-alpha, and superoxides of eosinophils. Only PGN could induce the degranulation for ECP release. However, ds poly I-C (TLR3 ligand), LPS (TLR4 ligand), ssRNA (TLR8 ligand), and CpG-DNA (TLR9 ligand) were much less effective or inactive. PGN, flagellin, and R837 could activate both nuclear factor (NF)-kappaB and extracellular signal-regulated protein kinase (ERK). PGN could activate phosphatidylinositol 3-kinase (PI3K)-Akt, and R837 both PI3K-Akt and p38 mitogen-activated protein kinase (MAPK). The induction of the release of IL-1beta, IL-6, IL-8, GRO-alpha, superoxides, and ECP by PGN, flagellin, and R837 was found to be differentially regulated by NF-kappaB, ERK, PI3K-Akt, and p38 MAPK. The above results therefore support that microbial infection may lead to the exacerbation of allergic inflammation.
Wong
Chun K
CK
Department of Chemical Pathology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, N.T., Hong Kong.
Cheung
Phyllis F Y
PF
Ip
Wai K
WK
Lam
Christopher W K
CW
D000634:Aminoquinolines / Q000494:pharmacology; D018821:CD18 Antigens / Q000096:biosynthesis; D002462:Cell Membrane / Q000378:metabolism; D054360:Chemokine CXCL1; D019743:Chemokines, CXC / Q000378:metabolism; D047150:Eosinophil Cationic Protein / Q000378:metabolism; D004804:Eosinophils / Q000166:cytology* / Q000378:metabolism; D006801:Humans; D000077271:Imiquimod; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism; D053583:Interleukin-1beta / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism; D016209:Interleukin-8 / Q000378:metabolism; D020935:MAP Kinase Signaling System; D009504:Neutrophils / Q000166:cytology; D015398:Signal Transduction; D051193:Toll-Like Receptors / Q000378:metabolism*
D000634:Aminoquinolines; D018821:CD18 Antigens; C475829:CXCL1 protein, human; D054360:Chemokine CXCL1; D019743:Chemokines, CXC; D053583:Interleukin-1beta; D015850:Interleukin-6; D016209:Interleukin-8; D051193:Toll-Like Receptors; D018799:Intercellular Adhesion Molecule-1; D047150:Eosinophil Cationic Protein; D000077271:Imiquimod