(PAF), a potent mediator of inflammation, by mononuclear phagocytes varies with their stage of cellular differentiation and the nature of the eliciting stimulus.
THEJOURNAL OF BIOLOGICAL CHEMISTRY (C
Vol. 266, No. 9, Issue of March 25, pp. 5472-5479,1991 Printed in U.S.A.
1991 by The American Society for Biochemistry and Molecular Biology, Inc.
Respiratory Syncytial Virus Infectionof Human Mononuclear Phagocytes StimulatesSynthesis of Platelet-activating Factor* (Received for publication, March 29, 1990)
Albert0 VillaniSB,Nick M. Cirinol, Elisabetta Baldiq, Mark KesterT,E. R. McFadden,Jr.t;, and James R. Panuskaz 11 From the $Airway Disease Center and the PDiuision of Nephrology of the Department of Medicine of University Hospitals and Case Western Reserve Uniuersity School of Medicine, Cleueland, Ohio 44106
Production of platelet-activating factor 1-0-alkyl2-acetyl-sn-glycero-3-phosphocholine (PAF), a potent mediator ofinflammation, by mononuclearphagocytes varies with their stage of cellular differentiation and the nature of the eliciting stimulus. The human monocytic cell line U937 can be induced to differentiate to a macrophage-like cellfollowing phorbol myristate acetate exposure, and after differentiation, these cells efficiently support replication of respiratory syncytial virus (RSV). US37 cells induced to differentiate with phorbol myristate acetate demonstrated a time-dependent decrease in PAF synthesis. RSV infection of these differentiated US37cells caused a sustained stimulation of PAF synthesis that paralleled viral replication and was dependent on infectious virus. Virus increased the activity of lyso-PAF:acetyl-CoA acetyltransferase (PAF acetyltransferase) in celllysates, thus enhancing the anabolic pathway of PAF synthesis without altering the activity of PAF acetylhydrolase, which regulates PAF catabolism. RSV infection of human monocytes also caused a marked increase in [3H] PAPproductioncompared to uninfected monocytes. Thus, virus infection serves as a novel stimulus to induce PAF synthesis in human mononuclear phagocytes and suggests that increased PAF production may have a critical role in the inflammatory response to RSV.
for a related group of ether- and ester-linkedglycerophospholipid compounds including both 1-0-acyl-2-acetyl-sn-glycero3-phosphocholine (1-0-acyl-GPC) and the potent biological mediator l-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (1-0-alkyl-GPC or PAF) (1-3). PAF has diverse biological effects which include aggregationand degranulationof platelets (1-3), accentuated chemotaxis and activationof neutrophils and peripheral blood mononuclear cells (4), enhanced vascular permeability (5), and decreased vascular tone (6). In addition, PAF modulates the cellular immune response (7), enhances the expression of Class I and I1 antigens of the major histocompatibility complex (8), increases cellular cytotoxicity (9), stimulates M P production of tumor necrosis factor, and regulates productionof interleukin 1 (10). These biological effects, together with the fact that PAF production is increased during sepsis or acute hypersensitivity reactions of acute inflam( l l ) , implicate PAF as an important mediator mation. Furthermore, a role for PAF in the lung has been suggested by in vivo studies demonstrating that PAF inhalation induces both bronchoconstriction and a prolonged increase in the sensitivityof the airways to react toexogenous stimuli (12, 13). Respiratory syncytial virus is the major causeof pulmonary inflammationininfants (14, 15). RSV-induced pulmonary inflammation results in bronchoconstriction and increased sensitivity of the airways to react to exogenous stimuli (14). The pathogenesis of these physiologic abnormalities may be Human mononuclear phagocytes(MP)’ are a major source related to productionof virus-specific IgE (16) and increased levels of histamine and leukotrienes in respiratory secretions * This work was supported by National Institutes of Health Spe- (16,17). The pulmonary cells that release these inflammatory cialized Center for Research in Airway Disease Grant HL 37117, mediators following RSV infectionhave not been determined, General Clinical Research Center Grant M01RR0080, and an Amernor is itknown if PAF hasa primary role in the inflammatory ican Lung Association Grant and a Thrasher Research Fund Grant response to this virus. However, in vitro studies have shown (to J. R. P.). Presented in part at the midwest section of the American Federation of Clinical Research, Chicago, Illinois, November, 1989, that human MP are susceptible to RSV infection (18) and and at theAmerican Thoracic Society, Boston, Massachusetts, May, support viral replication (19,20). Furthermore, RSV infection 1990. The costsof publication of this articlewere defrayed in partby of alveolar M P stimulates transcription and production of the payment of page charges. This article must therefore be hereby tumor necrosis factor (21), a cytokine capable of stimulating marked “advertisement” in accordance with 18 U.S.C. Section 1734 PAF production by leukocytes (22). Here we examined the solely to indicate this fact. effects of RSV on PAFmetabolism by MP. § Present address: The IV Cattedra di Clinica Pediatrica, UniverThe human U937 cell line (derivedfroma patient with sita’ “La Sapienza,”Rome, Italy. (1 To whom correspondence should be addressed Airway Disease histiocytic lymphoma (23)) has previously served as a useful Center, 2074 Abington Rd.,UniversityHospitals, Cleveland, OH model for studying the effects of differentiation of M P on 44106. metabolism (24-31). It is not known if ’ The abbreviationsused are: MP, mononuclear phagocytes; GPC, glycerophospholipid virus-infected M P have altered glycerophospholipid metabo2-acetyl-sn-glycero-3-phosphocholine; PAF, platelet-activating factor lism, but it has recently been shown that poliovirus infection or 1-0-alkyl-GPC;FCS,fetal calf serum;HEPES,4-(2-hydroxyethyl)-1-piperazineethanesulfonicacid HPTLC, high performance of HeLa cells enhances phospholipase C and depresses phosthin layer chromatography; PAF acetyltransferase,lyso-PAF:acetylpholipase AP activity (32); these alterations could effect the CoA acetyltransferase; PMA, phorbol myristate acetate; PBMC, peproduction of PAF. The effects of RSV on PAF metabolism ripheral blood mononuclear cells; HBSS, Hanks’ balanced salt soluin undifferentiated andphorbolmyristateacetate(PMA)tion; RSV, respiratory syncytial virus; BSA, bovine serum albumin; pfu, plaque-forming units; HPLC, high performance liquid chroma- differentiated U937 cells were examined. RSV infects only a few undifferentiated U937 cells (
