title: Human Leukocytes Kill Brugia malayi Microfilariae Independently of DNA-Based Extracellular Trap Release.
abstract: Wuchereria bancrofti, Brugia malayi and Brugia timori infect over 100 million people worldwide and are the causative agents of lymphatic filariasis. Some parasite carriers are amicrofilaremic whilst others facilitate mosquito-based disease transmission through blood-circulating microfilariae (Mf). Recent findings, obtained largely from animal model systems, suggest that polymorphonuclear leukocytes (PMNs) contribute to parasitic nematode-directed type 2 immune responses. When exposed to certain pathogens PMNs release extracellular traps (NETs) in the form of chromatin loaded with various antimicrobial molecules and proteases.
  
  
  
  In vitro, PMNs expel large amounts of NETs that capture but do not kill B. malayi Mf. NET morphology was confirmed by fluorescence imaging of worm-NET aggregates labelled with DAPI and antibodies to human neutrophil elastase, myeloperoxidase and citrullinated histone H4. A fluorescent, extracellular DNA release assay was used to quantify and observe Mf induced NETosis over time. Blinded video analyses of PMN-to-worm attachment and worm survival during Mf-leukocyte co-culture demonstrated that DNase treatment eliminates PMN attachment in the absence of serum, autologous serum bolsters both PMN attachment and PMN plus peripheral blood mononuclear cell (PBMC) mediated Mf killing, and serum heat inactivation inhibits both PMN attachment and Mf killing. Despite the effects of heat inactivation, the complement inhibitor compstatin did not impede Mf killing and had little effect on PMN attachment. Both human PMNs and monocytes, but not lymphocytes, are able to kill B. malayi Mf in vitro and NETosis does not significantly contribute to this killing. Leukocytes derived from presumably parasite-naïve U.S. resident donors vary in their ability to kill Mf in vitro, which may reflect the pathological heterogeneity associated with filarial parasitic infections.
  
  
  
  Human innate immune cells are able to recognize, attach to and kill B. malayi microfilariae in an in vitro system. This suggests that, in vivo, the parasites can evade this ability, or that only some human hosts support an infection with circulating Mf.
authors.affiliation: Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA, United States of America.|Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, GA, United States of America.
authors.forename: Ciaran J
authors.initials: CJ
authors.lastname: McCoy
authors.affiliation: Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA, United States of America.|Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, GA, United States of America.
authors.forename: Barbara J
authors.initials: BJ
authors.lastname: Reaves
authors.affiliation: Department of Large Animal Medicine, College of Veterinary Medicine, University of Georgia, Athens, GA, United States of America.
authors.forename: Steeve
authors.initials: S
authors.lastname: Giguère
authors.affiliation: Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA, United States of America.|Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, GA, United States of America.|Department of Biology & Biochemistry, University of Bath, Bath, United Kingdom.
authors.forename: Ruby
authors.initials: R
authors.lastname: Coates
authors.affiliation: Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA, United States of America.
authors.forename: Balázs
authors.initials: B
authors.lastname: Rada
authors.affiliation: Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA, United States of America.|Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, GA, United States of America.
authors.forename: Adrian J
authors.identifier: 0000-0001-7989-3929
authors.initials: AJ
authors.lastname: Wolstenholme
mesh_terms: D000818:Animals; D017178:Brugia malayi / Q000235:genetics / Q000276:immunology* / Q000502:physiology; D018509:DNA, Helminth / Q000235:genetics / Q000276:immunology*; D065206:Extracellular Traps / Q000276:immunology* / Q000469:parasitology; D005368:Filariasis / Q000276:immunology* / Q000469:parasitology; D005849:Gerbillinae; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000276:immunology; D008842:Microfilariae / Q000235:genetics / Q000276:immunology* / Q000502:physiology; D009504:Neutrophils / Q000276:immunology*
chemical_list: D018509:DNA, Helminth