Bovine blood derived macrophages are unable to control Coxiella burnetii replication under hypoxic conditions

Front Immunol. 2023 Jan 30:14:960927. doi: 10.3389/fimmu.2023.960927. eCollection 2023.

Abstract

Background: Coxiella burnetii is a zoonotic pathogen, infecting humans, livestock, pets, birds and ticks. Domestic ruminants such as cattle, sheep, and goats are the main reservoir and major cause of human infection. Infected ruminants are usually asymptomatic, while in humans infection can cause significant disease. Human and bovine macrophages differ in their permissiveness for C. burnetii strains from different host species and of various genotypes and their subsequent host cell response, but the underlying mechanism(s) at the cellular level are unknown.

Methods: C. burnetii infected primary human and bovine macrophages under normoxic and hypoxic conditions were analyzed for (i) bacterial replication by CFU counts and immunofluorescence; (ii) immune regulators by westernblot and qRT-PCR; cytokines by ELISA; and metabolites by gas chromatography-mass spectrometry (GC-MS).

Results: Here, we confirmed that peripheral blood-derived human macrophages prevent C. burnetii replication under oxygen-limiting conditions. In contrast, oxygen content had no influence on C. burnetii replication in bovine peripheral blood-derived macrophages. In hypoxic infected bovine macrophages, STAT3 is activated, even though HIF1α is stabilized, which otherwise prevents STAT3 activation in human macrophages. In addition, the TNFα mRNA level is higher in hypoxic than normoxic human macrophages, which correlates with increased secretion of TNFα and control of C. burnetii replication. In contrast, oxygen limitation does not impact TNFα mRNA levels in C. burnetii-infected bovine macrophages and secretion of TNFα is blocked. As TNFα is also involved in the control of C. burnetii replication in bovine macrophages, this cytokine is important for cell autonomous control and its absence is partially responsible for the ability of C. burnetii to replicate in hypoxic bovine macrophages. Further unveiling the molecular basis of macrophage-mediated control of C. burnetii replication might be the first step towards the development of host directed intervention measures to mitigate the health burden of this zoonotic agent.

Keywords: Coxiella burnetii; HIF1α; STAT3; TNF; bovine macrophages; citrate; hypoxia; normoxia.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cattle
  • Coxiella burnetii*
  • Cytokines / metabolism
  • Hypoxia / metabolism
  • Macrophages
  • Oxygen / metabolism
  • Q Fever*
  • Ruminants
  • Tumor Necrosis Factor-alpha / metabolism

Substances

  • Cytokines
  • Oxygen
  • Tumor Necrosis Factor-alpha

Grants and funding

This work was supported by the Deutsche Forschungsgemeinschaft (DFG) through the Collaborative Research Initiative 1181 (CRC1181) project A06 and by the Bundesministerium für Bildung und Forschung (BMBF) under the project number 01KI1726A/01KI2008A of “Q-GAPS” as part of the research network zoonotic infectious diseases to AL. KD was supported by the Bavarian Ministry of Science and the Arts within the Bavarian Research Network bayresq.net. IH was funded by the Bavarian Equal Opportunities Sponsorship – Realisierung von Chancengleichheit von Frauen in Forschung und Lehre (FFL) – Realization Equal Opportunities for Women in Research and Teaching.