title: Killer lymphocytes use granulysin, perforin and granzymes to kill intracellular parasites.
abstract: Protozoan infections are a serious global health problem. Natural killer (NK) cells and cytolytic T lymphocytes (CTLs) eliminate pathogen-infected cells by releasing cytolytic granule contents--granzyme (Gzm) proteases and the pore-forming perforin (PFN)--into the infected cell. However, these cytotoxic molecules do not kill intracellular parasites. CD8(+) CTLs protect against parasite infections in mice primarily by secreting interferon (IFN)-γ. However, human, but not rodent, cytotoxic granules contain the antimicrobial peptide granulysin (GNLY), which selectively destroys cholesterol-poor microbial membranes, and GNLY, PFN and Gzms rapidly kill intracellular bacteria. Here we show that GNLY delivers Gzms into three protozoan parasites (Trypanosoma cruzi, Toxoplasma gondii and Leishmania major), in which the Gzms generate superoxide and inactivate oxidative defense enzymes to kill the parasite. PFN delivers GNLY and Gzms into infected cells, and GNLY then delivers Gzms to the intracellular parasites. Killer cell-mediated parasite death, which we term 'microbe-programmed cell death' or 'microptosis', is caspase independent but resembles mammalian apoptosis, causing mitochondrial swelling, transmembrane potential dissipation, membrane blebbing, phosphatidylserine exposure, DNA damage and chromatin condensation. GNLY-transgenic mice are protected against infection by T. cruzi and T. gondii, and survive infections that are lethal to wild-type mice. Thus, GNLY-, PFN- and Gzm-mediated elimination of intracellular protozoan parasites is an unappreciated immune defense mechanism.
authors.affiliation: Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, Massachusetts, USA.|Department of Pediatrics, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Farokh
authors.initials: F
authors.lastname: Dotiwala
authors.affiliation: Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, Massachusetts, USA.|Department of Pediatrics, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Sachin
authors.initials: S
authors.lastname: Mulik
authors.affiliation: Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, Massachusetts, USA.|Department of Pediatrics, Harvard Medical School, Boston, Massachusetts, USA.|Fundação Oswaldo Cruz, Centro de Pesquisas René Rachou, Belo Horizonte, Brazil.
authors.forename: Rafael B
authors.identifier: http://orcid.org/0000-0003-2982-0072
authors.initials: RB
authors.lastname: Polidoro
authors.affiliation: Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, Massachusetts, USA.
authors.forename: James A
authors.initials: JA
authors.lastname: Ansara
authors.affiliation: Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, Massachusetts, USA.
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Burleigh
authors.affiliation: Department of Medicine, Université de Fribourg, Fribourg, Switzerland.
authors.forename: Michael
authors.initials: M
authors.lastname: Walch
authors.affiliation: Fundação Oswaldo Cruz, Centro de Pesquisas René Rachou, Belo Horizonte, Brazil.|Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, Massachusetts, USA.|Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts, USA.
authors.forename: Ricardo T
authors.initials: RT
authors.lastname: Gazzinelli
authors.affiliation: Program in Cellular and Molecular Medicine, Boston Children's Hospital, Boston, Massachusetts, USA.|Department of Pediatrics, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Judy
authors.initials: J
authors.lastname: Lieberman
mesh_terms: D000818:Animals; D000945:Antigens, Differentiation, T-Lymphocyte / Q000235:genetics / Q000276:immunology*; D014355:Chagas Disease / Q000276:immunology; D053804:Granzymes / Q000276:immunology*; D006801:Humans; D007694:Killer Cells, Natural / Q000276:immunology*; D018320:Leishmania major; D016773:Leishmaniasis, Cutaneous / Q000276:immunology; D051379:Mice; D008822:Mice, Transgenic; D054353:Perforin / Q000276:immunology*; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*; D014122:Toxoplasma; D014123:Toxoplasmosis / Q000276:immunology; D014349:Trypanosoma cruzi
chemical_list: D000945:Antigens, Differentiation, T-Lymphocyte; C075005:GNLY protein, human; D054353:Perforin; C509213:GZMB protein, human; D053804:Granzymes; C509212:GZMA protein, human