K. pneumoniae induced metabolic stress promotes immunotolerance

Metabolites generated in response to infection have a major role in shaping the nature of the immune response. We predicted that the metabolic response to the highly prevalent Klebsiella pneumoniae sequence type 258 (Kp ST258) strains is responsible for their ability to persist in the lungs, despite the expected proinflammatory signaling evoked by LPS. By combining in situ metabolic imaging and comprehensive transcriptional analyses, we demonstrate that Kp ST258 activates host glutaminolysis and fatty acid oxidation (FAO), generating an oxidant-rich microenvironment predisposed to the accumulation of anti-inflammatory monocyte populations. In a setting not unlike that generated by some tumors, metabolically active Kp ST258 elicits an immunotolerant, instead of a proinflammatory response. The bacteria in turn adapt to airway oxidants by upregulation of the Type VI Secretion System (T6SS), which is highly conserved across these strains worldwide. The global success of Kp ST258 can be explained, to a major extent, by their metabolic activity that promotes a permissive immune response to which the bacteria adapt. Dual RNA-seq experiment: Infection of wild type BL/6 and Irg1-/- (no itaconate produced) mice with K. pneumoniae MKP103 or PBS as control, Transcriptional data from bacteria isolated directly from murine lungs were compared to those from bacteria grown in Luria broth (control).