Macrophage development and activation involve coordinated intron retention in key inflammatory regulators

Monocytes and macrophages are essential components of the innate immune system. Herein, we report that intron retention (IR) plays an important role in the development and function of these cells. Using mRNA sequencing, bioinformatics analyses and RT-qPCR validation, we identified differential IR and altered expression of key genes involved in macrophage development and function, both in vitro and in vivo. We demonstrate that decreased IR in nuclear-detained mRNA is coupled to increased expression of genes encoding regulators of macrophage transcription, phagocytosis and inflammatory signalling, including ID2, IRF7, ENG and LAT. We further show that this dynamic IR program persists during the polarisation of resting macrophages into activated macrophages. In the presence of proinflammatory stimuli, intron-retaining CXCL2 and NFKBIZ transcripts in macrophages are rapidly spliced, leading to timely expression of these key inflammatory regulators by macrophages. Our study provides novel insights into the molecular mechanisms controlling vital regulators of the innate immune response.