Complement C5a is a key mediator of meconium-induced neutrophil activation.
Meconium aspiration syndrome is a serious condition of the newborn characterized by pulmonary inflammation with substantial neutrophil infiltration. We recently showed that meconium is a potent activator of complement. The aim of the present study was to investigate a possible role for complement in meconium-induced neutrophil activation. Meconium was incubated in human whole blood anticoagulated with lepirudin, a specific thrombin inhibitor that does not affect complement activation. Complement activation was detected by measuring the terminal complement complex. Neutrophil oxidative burst and changes in CD11b and L-selectin expression were measured by flow cytometry. Complement was inhibited using the MAb 166-32 and 137-26, which block factor D and neutralize C5a, respectively. Meconium markedly activated the neutrophils, as revealed by up-regulation of CD11b, accentuation of L-selectin shedding, and induction of oxidative burst. Complement inhibition using the anti-factor D antibody completely (95-100%) blocked meconium-induced changes in CD11b and L-selectin expression, whereas oxidative burst was reduced by 60-70%. The anti-C5a antibody inhibited the neutrophil activation to the same extent as anti-factor D. The data suggest that complement activation is largely responsible for the neutrophil inflammatory responses induced by meconium in vitro and that C5a is a key mediator of this response.
Castellheim
Albert
A
Department of Pediatric Research, Rikshospitalet University Hospital, 0027 Oslo, Norway. albert.castellheim@klinmed.uio.no
Pharo
Anne
A
Fung
Michael
M
Saugstad
Ola D
OD
Mollnes
Tom E
TE
D000911:Antibodies, Monoclonal / Q000737:chemistry; D039481:CD11b Antigen / Q000096:biosynthesis; D003167:Complement Activation; D015936:Complement C5a / Q000737:chemistry* / Q000502:physiology*; D003165:Complement System Proteins / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry; D006629:Hirudins / Q000031:analogs & derivatives* / Q000494:pharmacology; D006801:Humans; D007231:Infant, Newborn; D007249:Inflammation; D019041:L-Selectin / Q000096:biosynthesis; D008470:Meconium / Q000378:metabolism*; D008471:Meconium Aspiration Syndrome / Q000473:pathology*; D018375:Neutrophil Activation; D009504:Neutrophils / Q000378:metabolism*; D018384:Oxidative Stress; D011485:Protein Binding; D011994:Recombinant Proteins / Q000494:pharmacology; D016897:Respiratory Burst; D013577:Syndrome
D000911:Antibodies, Monoclonal; D039481:CD11b Antigen; D006629:Hirudins; D011994:Recombinant Proteins; D019041:L-Selectin; D015936:Complement C5a; D003165:Complement System Proteins; C083544:lepirudin