Elevated CO2 suppresses specific Drosophila innate immune responses and resistance to bacterial infection

Iiro Taneli Helenius, Thomas Krupinski, Douglas W. Turnbull, Yosef Gruenbaum, Neal Silverman, Eric A. Johnson, Peter H S Sporn, Jacob I. Sznajder, Greg J. Beitel

Research output: Contribution to journalArticlepeer-review

54 Scopus citations

Abstract

Elevated CO2 levels (hypercapnia) frequently occur in patients with obstructive pulmonary diseases and are associated with increased mortality. However, the effects of hypercapnia on non-neuronal tissues and the mechanisms that mediate these effects are largely unknown. Here, we develop Drosophila as a genetically tractable model for defining non-neuronal CO2 responses and response pathways. We show that hypercapnia significantly impairs embryonic morphogenesis, egg laying, and egg hatching even in mutants lacking the Gr63a neuronal CO2 sensor. Consistent with previous reports that hypercapnic acidosis can suppress mammalian NF-κB-regulated innate immune genes, we find that in adult flies and the phagocytic immune-responsive S2* cell line, hypercapnia suppresses induction of specific antimicrobial peptides that are regulated by Relish, a conserved Rel/NF-κB family member. Correspondingly, modest hypercapnia (7-13%) increases mortality of flies inoculated with E. faecalis, A. tumefaciens, or S. aureus. During E. faecalis and A. tumefaciens infection, increased bacterial loads were observed, indicating that hypercapnia can decrease host resistance. Hypercapnic immune suppression is not mediated by acidosis, the olfactoryCO2 receptor Gr63a, or by nitric oxide signaling. Further, hypercapnia does not induce responses characteristic of hypoxia, oxidative stress, or heat shock. Finally, proteolysis of the Relish IκB-like domain is unaffected by hypercapnia, indicating that immunosuppression acts downstream of, or in parallel to, Relish proteolytic activation. Our results suggest that hypercapnic immune suppression is mediated by a conserved response pathway, and illustrate a mechanism by which hypercapnia could contribute to worse outcomes of patients with advanced lung disease, who frequently suffer from both hypercapnia and respiratory infections.

Original languageEnglish (US)
Pages (from-to)18710-18715
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume106
Issue number44
DOIs
StatePublished - Nov 3 2009

Keywords

  • COPD
  • Gr63a
  • Hypercapnia
  • NF-κB
  • Relish

ASJC Scopus subject areas

  • General

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