SMPDL3B (sphingomyelin phosphodiesterase acid-like 3B) is a lipid-modulating phosphodiesterase primarily expressed on macrophages, dendritic cells, and podocytes that serves as a negative regulator of inflammatory signaling 1. The enzyme functions through multiple mechanisms: it acts as a cGAMP hydrolase that suppresses cGAS-STING antiviral signaling 2, regulates sphingolipid metabolism through ceramide and sphingosine-1-phosphate pathways 3, and modulates membrane lipid raft integrity critical for barrier function 4. SMPDL3B is stabilized through palmitoylation by ZDHHC5 in response to high glucose conditions 5. Disease relevance spans multiple pathologies: in diabetic retinopathy, SMPDL3B silencing exacerbates vascular endothelial inflammation via NF-κB/NLRP3 activation 5; reduced expression associates with focal segmental glomerulosclerosis susceptibility and podocyte injury 6; altered expression contributes to Alport Syndrome proteinuria and podocyte dysfunction 3; and elevated levels predict poor prognosis in acute myeloid leukemia 7. Emerging evidence identifies circulating SMPDL3B as a biomarker for myalgic encephalomyelitis severity and immune dysregulation, with potential therapeutic targeting via PI-PLC inhibition 84.