CLOCK and pneumonia: In addition, the REV-ERB isoforms repress the expression of the Mmp9 and Cxc3cr1 genes, which regulate cellular infiltration and migration, by inhibiting the transcription of their non-coding RNAs that act as enhancers in murine macrophage lineages, including bone marrow-derived and peritoneal exudate macrophages (Lam et al., 2013), strongly indicating that the degree of monocyte infiltration during pulmonary infection and the resulting pathogen clearance and/or pneumonia are also controlled by the circadian clock.