The functions of Nr4a1-dependent Ly6C^low monocytes remain enigmatic. We show that they are enriched within capillaries and scavenge microparticles from their lumenal side in a steady state. In the kidney cortex, perturbation of homeostasis by a TLR7-dependent nucleic acid "danger" signal, which may signify viral infection or local cell death, triggers Gαi-dependent intravascular retention of Ly6C^low monocytes by the endothelium. Then, monocytes recruit neutrophils in a TLR7-dependent manner to mediate focal necrosis of endothelial cells, whereas the monocytes remove cellular debris. Prevention of Ly6C^low monocyte development, crawling, or retention in Nr4a1^−/−, Itgal^−/−, and Tlr7^{host−/−BM+/+} and Cx3cr1^−/− mice, respectively, abolished neutrophil recruitment and endothelial killing. Prevention of neutrophil recruitment in Tlr7^{host+/+BM−/−} mice or by neutrophil depletion also abolished endothelial cell necrosis. Therefore, Ly6C^low monocytes are intravascular housekeepers that orchestrate the necrosis by neutrophils of endothelial cells that signal a local threat sensed via TLR7 followed by the in situ phagocytosis of cellular debris.