FIG 4.
K. pneumoniae interactions with host innate immune cells. Each panel depicts our current understanding of how different K. pneumoniae strains interact with host innate immune cells, based largely on in vitro and animal infection studies. Differences between a widely used laboratory strain (KPPR1), hypervirulent clinical isolates (hvKp), and carbapenem-resistant isolates (CR-Kp) are shown. Black arrows show induction or activation, while red T-bars show inhibition. Question marks indicate interactions that remain to be fully elucidated. The depictions of proinflammatory and anti-inflammatory monocytes show how these cells have been observed to respond to K. pneumoniae in the lungs of mice during pneumonia. In the case of anti-inflammatory monocytes, K. pneumoniae infection promotes the expansion of these cells, which can either temper the inflammatory response and minimize lung injury at early time points during CR-Kp infection, or mediate the efferocytosis of apoptotic neutrophils and injury resolution at later time points during KPPR1 infection. In both cases, these anti-inflammatory effects are mediated by IL-10.