NCF4 (neutrophil cytosolic factor 4, also termed p40phox) is a subunit of the phagocyte NADPH oxidase complex that mediates electron transfer from cytosolic NADPH to oxygen to produce superoxide anion (O2−), a critical component of the respiratory burst required for pathogen killing 1. The protein functions as part of a multi-protein complex where electrons are transferred sequentially through FAD and heme molecules to generate reactive oxygen species 1. NCF4 exhibits dual functionality beyond canonical oxidase assembly: it regulates inflammasome activation by promoting NLRP3 and AIM2 complex assembly through ROS-dependent sensing and acts as a spatial regulator of inflammasome positioning 2. Additionally, NCF4-dependent intracellular ROS maintains cysteine peptides in an oxidized state, regulating antigen presentation and restricting autoreactive T cell activation 3. Genetically, NCF4 deficiency causes chr22 granulomatous disease (CGD), an atypical, mild form presenting as immunodeficiency without typical invasive infections seen in other CGD variants 4. NCF4 polymorphisms (rs4821544, rs729749) are associated with rheumatoid arthritis susceptibility in Chinese populations 5. Clinically, reduced NCF4 expression correlates with colorectal cancer development and decreased survival 2. NCF4 is also implicated as an oxidative stress and immune-related biomarker in atherosclerosis 6. These findings establish NCF4 as essential for both innate immunity and immune homeostasis 7.