Effect of enterohaemorrhagic E scherichia coli O 157: H 7‐specific enterohaemolysin on interleukin‐1 β production differs between human and mouse macrophages due to the different sensitivity of NLRP 3 activation

Summary Enterohaemorrhagic E scherichia coli ( EHEC ) O157:H7 infection in humans can cause acute haemorrhagic colitis and severe haemolytic uraemic syndrome. The role of enterohaemolysin (Ehx) in the pathogenesis of O157:H7‐mediated disease in humans remains undefined. Recent studies have revealed the importance of the inflammatory response in O157:H7 pathogenesis in humans. We previously reported that Ehx markedly induced interleukin‐1 β ( IL ‐1 β ) production in human macrophages. Here, we investigated the disparity in Ehx‐induced IL ‐1 β production between human and mouse macrophages and explored the underlying mechanism regarding the activation of NOD ‐like receptor family, pyrin domain containing 3 ( NLRP 3) inflammasomes. In contrast to the effects on human differentiated THP ‐1 cells and peripheral blood mononuclear cells, Ehx exerted no effect on IL ‐1 β production in mouse macrophages and splenocytes because of a disparity in pro‐ IL ‐1 β cleavage into mature IL ‐1 β upon caspase‐1 activation. Additionally, Ehx significantly contributed to O157:H7‐induced ATP release from THP ‐1 cells, which was not detected in mouse macrophages. Confocal microscopy demonstrated that Ehx was a key inducer of cathepsin B release in THP ‐1 cells but not in mouse IC ‐21 cells upon O157:H7 challenge. Inhibitor experiments indicated that O157:H7‐induced IL ‐1 β production was largely dependent upon caspase‐1 activation and partially dependent upon ATP signalling and cathepsin B release, which were both involved in NLRP 3 activation. Moreover, inhibition of K + efflux drastically diminished O157:H7‐induced IL ‐1 β production and cytotoxicity. The findings in this study may shed light on whether and how the Ehx contributes to the development of haemolytic uraemic syndrome in human O157:H7 infection.