CD200R1 is an inhibitory receptor that plays a crucial role in limiting inflammation by negatively regulating immune cell activation. The receptor binds to its ligand CD200 and inhibits expression of pro-inflammatory molecules including TNF, interferons, and inducible nitric oxide synthase in response to selected stimuli 1. CD200R1 is predominantly expressed on microglia and macrophages, where it maintains cellular quiescence and prevents abnormal activation 2. The receptor's expression is transcriptionally regulated by NFKB1, and reduced CD200R1 levels correlate with microglial overactivation in neurological disorders like Parkinson's disease 2. CD200R1 serves as a specific marker for M2 alternatively activated macrophages, distinguishing them from pro-inflammatory M1 macrophages 3. The CD200-CD200R1 signaling pathway facilitates resolution of inflammation, with CD200R1-expressing cells clustering in pro-resolving tissue niches 4. Expression of both CD200 and CD200R1 is important for maintaining successful pregnancy, as decreased levels are associated with spontaneous early abortion 5. The pathway is also enriched in pathogenic Th2 cells in allergic airway diseases 6.