Retinoid X receptor a controls innate inflammatory responses through the up-regulation of chemokine expression

The retinoid X receptor a (RXRa) plays a central role in the regulation of many intracellular receptor signaling pathways and can mediate ligand-dependent transcription by forming homodimers or heterodimers with other nuclear receptors. Although several members of the nuclear hormone receptor superfamily have emerged as important regulators of macrophage gene expression, the existence in vivo of an RXR signaling pathway in macrophages has not been established. Here, we provide evidence that RXRa regulates the transcription of the chemokines Ccl6 and Ccl9 in macrophages independently of heterodimeric partners. Mice lacking RXRa in myeloid cells exhibit reduced levels of CCL6 and CCL9, impaired recruitment of leukocytes to sites of inflammation, and lower susceptibility to sepsis. These studies demonstrate that macrophage RXRa plays key roles in the regulation of innate immunity and represents a potential target for immunotherapy of sepsis.