BPIFA2 (BPI fold containing family A member 2) is a secreted antimicrobial protein with pleiotropic functions in mucosal immunity and kidney pathology. Primary function: BPIFA2 demonstrates strong antibacterial activity against Pseudomonas aeruginosa and is normally expressed in parotid glands, abundant in salivary secretions 1. Mechanism: The protein functions as a lipopolysaccharide-binding, antimicrobial peptide localized to extracellular regions and exosomes [UniProt]. Under pathological conditions, BPIFA2 expression is induced in renal tubular epithelial cells, where it interacts with LRP5 to promote mitochondrial dysfunction and kidney injury 2. Disease relevance: BPIFA2 serves as an early biomarker for acute kidney injury (AKI), appearing in plasma and urine within 6 hours of renal injury 1. Expression is significantly elevated in lupus nephritis patients and correlates with renal injury severity 2. BPIFA2 levels are altered during head and neck cancer radiotherapy, associated with mucositis and hyposalivation 34. High serum autoantibodies against BPIFA2 occur in 67% of APECED patients with sicca symptoms, associated with earlier-onset oral dryness 5. Clinical significance: BPIFA2 represents a promising early diagnostic biomarker for AKI and a potential therapeutic target for lupus nephritis, warranting further clinical investigation 62.