MMD2 (monocyte to macrophage differentiation associated 2) is a member of the progestin and adipoQ receptor (PAQR) family with critical roles in immune cell function and innate immunity. MMD2 localizes to the Golgi apparatus and perinuclear cytoplasm 1, where it regulates protein kinase activity and Ras/ERK signaling pathways 1. The protein is expressed during testis development and operates downstream of known sex-determining genes 2, though functional redundancy within the PAQR family may limit its individual developmental requirement 2. Clinically, MMD2 dysfunction has significant pathological consequences. Monoallelic mutations in MMD2 (p.A116V and p.R126P) cause autosomal dominant aggressive periodontitis by impairing fMLP-induced neutrophil chemotaxis and Ras/ERK activation, leading to alveolar bone loss 1. Additionally, MMD2 upregulation promotes malignancy in gastric and breast cancers through dysregulation of the miR-509-3p and miR-1270 pathways, respectively 32. In lung cancer, MMD2 expression correlates with tumor microenvironment composition and serves as a biomarker for prognosis and immunotherapy response 4. These findings establish MMD2 as an important regulator of innate immunity and a potential therapeutic target in inflammatory and malignant diseases.