title: Secondary necrotic neutrophils release interleukin-16C and macrophage migration inhibitory factor from stores in the cytosol.
abstract: Neutrophils harbor a number of preformed effector proteins that allow for immediate antimicrobial functions without the need for time-consuming de novo synthesis. Evidence indicates that neutrophils also contain preformed cytokines, including interleukin (IL)-1ra, CXCL8 and CXCL2. In the search for additional preformed cytokines, a cytokine array analysis identified IL-16 and macrophage migration inhibitory factor (MIF) as preformed cytokines in lysates from human primary neutrophils. Both IL-16 and MIF are unconventional cytokines because they lack a signal sequence. Using confocal immunofluorescence microscopy as well as western blot analysis of subcellular fractions, IL-16 and MIF were found to be stored in the cytosol rather than in the granules of human neutrophils, which implies an unconventional secretion mechanism for both cytokines. IL-16 is synthesized and stored as a precursor (pre-IL-16). We present evidence that the processing of pre-IL-16 to the biologically active IL-16C is mediated by caspase-3 and occurs during both spontaneous and UV-induced apoptosis of human neutrophils. Although IL-16 processing occurs during apoptosis, IL-16C and MIF release was observed only during secondary necrosis of neutrophils. Screening a panel of microbial substances and proinflammatory cytokines did not identify a stimulus that induced the release of IL-16C and MIF independent of secondary necrosis. The data presented here suggest that IL-16 and MIF are neutrophil-derived inflammatory mediators released under conditions of insufficient clearance of apoptotic neutrophils, as typically occurs at sites of infection and autoimmunity.
authors.affiliation: Institute for Medical Microbiology and Hygiene, University of Lübeck , Ratzeburger Allee 160, Lübeck 23562, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Roth
authors.affiliation: Institute for Medical Microbiology and Hygiene, University of Lübeck , Ratzeburger Allee 160, Lübeck 23562, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Agthe
authors.affiliation: Institute for Medical Microbiology and Hygiene, University of Lübeck , Ratzeburger Allee 160, Lübeck 23562, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Eickhoff
authors.affiliation: Institute for Medical Microbiology and Hygiene, University of Lübeck , Ratzeburger Allee 160, Lübeck 23562, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Möller
authors.affiliation: Institute for Systemic Inflammation Research, University of Lübeck , Ratzeburger Allee 160, Lübeck 23562, Germany.
authors.forename: C M
authors.initials: CM
authors.lastname: Karsten
authors.affiliation: Department of Hematology, Granulocyte Research Laboratory , L-4041, Finsen Center, The National University Hospital, 9 Blegdamsvej, Copenhagen DK-2100, Denmark.
authors.forename: N
authors.initials: N
authors.lastname: Borregaard
authors.affiliation: Institute for Medical Microbiology and Hygiene, University of Lübeck , Ratzeburger Allee 160, Lübeck 23562, Germany.
authors.forename: W
authors.identifier: 0000-0002-3608-8652
authors.initials: W
authors.lastname: Solbach
authors.affiliation: Institute for Medical Microbiology and Hygiene, University of Lübeck , Ratzeburger Allee 160, Lübeck 23562, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Laskay