The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that senses environmental toxins and endogenous ligands to induce detoxifying enzymes and modulate differentiation of cells of the immune system. In Nature, Kaufmann and colleagues show that AhR is a receptor for bacterial pigments and induces the production of cytokines and chemokines as part of the antibacterial immune response. Pigmented virulence factors such as phenazines from Pseudomonas aeruginosa bind AhR and activate the detoxification pathway. During infection of mice with P. aeruginosa, AhR signaling is required in neutrophils and macrophages as well as in respiratory epithelial cells for the induction of proinflammatory cytokines and chemokines, neutrophil recruitment and mucus production. AhR-deficient mice are more sensitive to infection with P. aeruginosa and Mycobacterium tuberculosis. Thus, AhR functions as an intracellular pattern-recognition receptor for bacterial pigments, which can be defined as a new class of pathogen-associated molecular patterns.

Nature (13 August 2014) 10.1038/nature13684