title: Activation of human mast cells through the platelet-activating factor receptor.
abstract: BACKGROUND
  In human subjects platelet-activating factor (PAF) concentrations are markedly increased in the plasma after anaphylactic reactions, and these correlate strongly with the severity of the response. The mechanism for the systemic spread of mast cell (MC) activation in anaphylaxis is often assumed to relate to the hematogenous spread of allergen, but this is implausible, and amplification mechanisms need to be considered.
  
  
  OBJECTIVE
  We have investigated the ability of PAF to induce human MC degranulation using skin, lung, and peripheral blood (PB)-derived cultured MCs and the signaling pathways activated in PB-derived MCs in response to PAF.
  
  
  METHODS
  The expression of PAF receptor was investigated by means of RT-PCR and Western blot analysis. Cell-signaling pathways in PB-derived MCs in response to PAF were investigated by analyzing the effect of various inhibitors and the silencing of phospholipase C (PLC) mRNA on PAF-mediated histamine release.
  
  
  RESULTS
  We show for the first time that PAF induces histamine release from human lung MCs and PB-derived MCs but not skin MCs. Activation of PAF receptor-coupled G(alphai) leads to degranulation through PLCgamma1 and PLCbeta2 activation in human MCs. PAF-induced degranulation was rapid, being maximal at 5 seconds, and was partially dependent on extracellular Ca(2+).
  
  
  CONCLUSIONS
  Our findings provide a mechanism whereby PAF mediates an amplification loop for MC activation in the generation of anaphylaxis.
authors.affiliation: Division of Molecular Cell Immunology and Allergology, Advanced Medical Research Center, Nihon University Graduate School of Medical Science, Tokyo 173-8610, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Kajiwara
authors.forename: Tomomi
authors.initials: T
authors.lastname: Sasaki
authors.forename: Peter
authors.initials: P
authors.lastname: Bradding
authors.forename: Glenn
authors.initials: G
authors.lastname: Cruse
authors.forename: Hironori
authors.initials: H
authors.lastname: Sagara
authors.forename: Kazumitsu
authors.initials: K
authors.lastname: Ohmori
authors.forename: Hirohisa
authors.initials: H
authors.lastname: Saito
authors.forename: Chisei
authors.initials: C
authors.lastname: Ra
authors.forename: Yoshimichi
authors.initials: Y
authors.lastname: Okayama
mesh_terms: D000707:Anaphylaxis / Q000276:immunology / Q000503:physiopathology; D002478:Cells, Cultured; D006636:Histamine Release; D006801:Humans; D008168:Lung / Q000166:cytology; D008407:Mast Cells / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D010972:Platelet Activating Factor / Q000378:metabolism*; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D012867:Skin / Q000166:cytology
chemical_list: D010972:Platelet Activating Factor; D010980:Platelet Membrane Glycoproteins; D043562:Receptors, G-Protein-Coupled; C039351:platelet activating factor receptor