Strain- and host species-specific inflammasome activation, IL-1β release, and cell death in macrophages infected with uropathogenic Escherichia coli
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Uropathogenic Escherichia coli (UPEC) is the main etiological agent of urinary tract infections (UTIs). Little is known about interactions between UPEC and the inflammasome, a key innate immune pathway. Here we show that UPEC strains CFT073 and UTI89 trigger inflammasome activation and lytic cell death in human macrophages. Several other UPEC strains, including two multidrug-resistant ST131 isolates, did not kill macrophages. In mouse macrophages, UTI89 triggered cell death only at a high multiplicity of infection, and CFT073-mediated inflammasome responses were completely NLRP3-dependent. Surprisingly, CFT073- and UTI89-mediated responses only partially depended on NLRP3 in human macrophages. In these cells, NLRP3 was required for interleukin-1ߠ(IL-1ߩ maturation, but contributed only marginally to cell death. Similarly, caspase-1 inhibition did not block cell death in human macrophages. In keeping with such differences, the pore-forming toxin a-hemolysin mediated a substantial proportion of CFT073-triggered IL-1ߠsecretion in mouse but not human macrophages. There was also a more substantial a-hemolysin-independent cell death response in human vs. mouse macrophages. Thus, in mouse macrophages, CFT073-triggered inflammasome responses are completely NLRP3-dependent, and largely a-hemolysin-dependent. In contrast, UPEC activates an NLRP3-independent cell death pathway and an a-hemolysin-independent IL-1ߠsecretion pathway in human macrophages. This has important implications for understanding UTI in humans.
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