TLR2 signaling in tubular epithelial cells regulates NK cell recruitment in kidney ischemia-reperfusion injury.

Damage-associated molecular patterns released from damaged kidney cells initiate postischemic inflammation, an essential step in the progression of kidney ischemia-reperfusion injury (IRI). However, the mechanism that coordinates this highly specific process in ischemic kidneys remains to be clarified. Previously, we demonstrated that CD137 from NK cells specifically stimulates CD137 ligand (CD137L) on tubular epithelial cells (TECs) such that TECs produced the high CXCR2 chemokine levels required for neutrophil chemotaxis. We report in the present study that endogenous TLR2 ligands released from ischemic TECs induce CCR5 chemokine expression, which is critical to promoting NK cell recruitment. By implanting CD137L(-/-) TECs into the kidney capsule of TLR2(-/-) mice, we further showed that TLR2-mediated NK cell recruitment is an uncoupled event that can occur independently of CD137L signaling in TECs, which is responsible for recruiting neutrophils. Therefore, our findings identify TECs as both a target for kidney damage and also as a master regulator that actively modulates stepwise signaling, leading to the initiation and amplification of acute sterile inflammation that inflicts kidney IRI. Being clinically important, the signaling pathway of innate receptors in epithelial cells may therefore be a good target to block acute sterile inflammation resulting from tissue damage, including kidney IRI.