title: The induction and augmentation of macrophage tumoricidal responses by platelet-activating factor.
abstract: Platelet-activating factor (PAF) has previously been shown to stimulate intracellular signal transductional events similar to the macrophage tumoricidal activators interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS). Macrophages stimulated with IFN-gamma and LPS utilize various cytolytic mediators in order to kill tumor cells. However, PAF has been shown to only induce and enhance tumor necrosis factor-alpha (TNF alpha)-mediated cytolysis by macrophages. Therefore, the purpose of this study was to determine whether PAF, in comparison with IFN-gamma and LPS, could stimulate macrophages for both TNF alpha- and non-TNF alpha-mediated tumoricidal activity. For this, the activation of macrophages for a cytolytic response was characterized by the production of TNF alpha and nitric oxide (NO2-), as well as, their ability to kill select tumor cells. PAF together with IFN-gamma stimulated macrophage secretion of NO2-. In addition, PAF enhanced IFN-gamma- and LPS-stimulated NO2- production. PAF, together with IFN-gamma, also activated macrophages for tumoricidal activity against TNF alpha-resistant tumor cells. In assays to determine the temporal sequence of activation, increased tumor cell cytolysis was observed only when macrophages were first treated with IFN-gamma. Moreover, PAF enhanced macrophage tumoricidal activity when added with LPS and IFN-gamma. With respect to TNF alpha production, macrophages activated with high concentrations of PAF stimulated significant levels of TNF alpha compared to macrophages without PAF. A similar level was observed following multiple additions of a lower concentration of PAF. Also, PAF induced macrophage cytolytic activity against a TNF alpha-sensitive tumor cell. In addition, PAF significantly enhanced LPS-induced TNF alpha production. Thus, PAF can play a modulatory role in the activation for non-TNF alpha-mediated tumoricidal activity of macrophages.
authors.affiliation: Department of Cell Biology and Human Anatomy, School of Medicine, University of California, Davis 95616-8643, USA.
authors.forename: A D
authors.initials: AD
authors.lastname: Howard
authors.forename: K L
authors.initials: KL
authors.lastname: Erickson
mesh_terms: D000818:Animals; D003602:Cytotoxicity, Immunologic / Q000187:drug effects; D004306:Dose-Response Relationship, Immunologic; D005260:Female; D008262:Macrophage Activation / Q000187:drug effects*; D051379:Mice; D008810:Mice, Inbred C57BL; D009374:Neoplasms, Experimental / Q000276:immunology; D009569:Nitric Oxide / Q000096:biosynthesis; D010972:Platelet Activating Factor / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000032:analysis / Q000187:drug effects / Q000378:metabolism
chemical_list: D010972:Platelet Activating Factor; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide