The emerging roles of NFIL3 in immunity.

NFIL3 (E4BP4) is a basic leucine zipper transcription factor best known for its roles in circadian regulation. It functions primarily as a transcriptional repressor through competitive DNA binding and the recruitment of histone-modifying complexes. More recently, NFIL3 has emerged as a critical regulator of immunity. It is essential for the development of multiple immune cell subsets, including NK cells and CD8+ dendritic cells, and modulates the activity of many others. For instance, NFIL3 influences B cell class switching and cytokine production in T helper subsets and macrophages. Its expression is dynamically controlled by cytokines and environmental signals, positioning NFIL3 as a key integrator of circadian and immune pathways. Consistent with these roles, recent studies have implicated NFIL3 in multiple immune-mediated diseases, including colitis, lupus, and arthritis. In this review, we highlight NFIL3's immunological functions, its evolutionary conservation, and its emerging role as a context-dependent modulator of inflammation and immune homeostasis.