Azurocidin (AZU1), encoded on chromosome 19p13.3 within a gene cluster alongside proteinase 3 and neutrophil elastase, is a glycoprotein belonging to the serine protease family but lacking enzymatic activity due to mutations in its catalytic triad (His41Ser, Ser175Gly). This pseudoenzyme exerts multifunctional roles in innate immunity, primarily through its N-terminal hydrophobic pocket (residues 20–44), which binds Gram-negative bacterial lipid A for antimicrobial activity, and a cationic domain mediating heparin interactions. As a key inflammatory mediator, azurocidin induces endothelial permeability via paracrine signaling, facilitating leukocyte extravasation by creating intercellular gaps, while also acting as a monocyte chemoattractant via formyl-peptide receptors and β2-integrins.