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Many respiratory infections are selectively injurious to infants, yet the etiology of age-associated susceptibility is unknown. One such bacterial pathogen is Bordetella pertussis. In adult mice, innate interferon γ (IFN-γ) is produced by natural killer (NK) cells and restricts infection to the respiratory tract. In contrast, infant pertussis resembles disease in NK cell– and IFN-γ–deficient adult mice that experience disseminated lethal infection. We hypothesized that infants exhibit age-associated deficits in NK cell frequency, maturation, and responsiveness to B. pertussis , associated with low IFN-γ levels. To delineate mechanisms behind age-dependent susceptibility, we compared infant and adult mouse models of infection. Infection in infant mice resulted in impaired upregulation of IFN-γ and substantial bacterial dissemination. B. pertussis –infected infant mice displayed fewer pulmonary NK cells than adult mice. Furthermore, the NK cells in the infant mouse lungs had an immature phenotype, and the infant lung showed no upregulation of the IFN-γ–inducing cytokine IL-12p70. Adoptive transfer of adult NK cells into infants, or treatment with exogenous IFN-γ, significantly reduced bacterial dissemination. These data indicate that the lack of NK cell–produced IFN-γ significantly contributes to infant fulminant pertussis and could be the basis for other pathogen-induced, age-dependent respiratory diseases. [ABSTRACT FROM AUTHOR]

Interferon lambda (IFN-λ) plays diverse roles in bacterial infections. Previously we showed that IFN-λ is induced in the lungs of B. pertussis-infected adult mice and exacerbates inflammation. Here, we report that mice lacking the IFN-λ receptor (IFNLR1) specifically on neutrophils (MRP8creIFNLR1fl/fl mice) exhibit reduced lung bacterial load and inflammation compared to WT mice during B. pertussis infection. In B. pertussis-infected wild type (WT) mice, lung type I and III IFN responses were higher than in MRP8creIFNLR1fl/fl mice, correlating with increased lung inflammatory pathology. There was an increased proportion of IFN-γ-producing neutrophils in the lungs of MRP8creIFNLR1fl/fl mice compared to WT mice. IFNLR1-/- neutrophils incubated with B. pertussis exhibited higher killing compared to WT neutrophils. Treatment of WT neutrophils with IFN-λ further decreased their bacterial killing capacity and treatment of WT mice with IFN-λ increased lung bacterial loads. Contributing to the differential killing, we found that IFNLR1-/- neutrophils exhibit higher levels of reactive oxygen species, myeloperoxidase [1], matrix metalloproteinase-9 (MMP9) activity, neutrophil extracellular traps (NETs), and IFN-γ secretion than WT neutrophils, and inhibiting NADPH oxidase inhibited bacterial killing in IFNLR1-/- neutrophils. B. pertussis induced IFN-λ secretion and IFNLR1 gene expression in mouse and human neutrophils and this was dependent on the bacterial virulence protein pertussis toxin (PTX). PTX enhanced bacterial loads in WT but not in MRP8creIFNLR1fl/fl or IFNLR1-/- mice. Thus, PTX disrupts neutrophil function by enhancing type III IFN signaling, which prevents neutrophils from effectively clearing B. pertussis during infection, leading to higher bacterial loads and exacerbation of lung inflammation., (© The Author(s) 2024. Published by Oxford University Press on behalf of Society for Leukocyte Biology. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)