PGLYRP4 is a peptidoglycan recognition protein functioning as a pattern recognition receptor in innate immunity 1. As a secreted protein expressed on body surfaces, mucous membranes, and in secretions including saliva and sweat 1, PGLYRP4 recognizes bacterial peptidoglycan and exerts direct bactericidal activity against Gram-positive bacteria and bacteriostatic activity toward Gram-negative bacteria 2. Unlike PGLYRP2, PGLYRP4 lacks enzymatic activity and kills bacteria by interacting with cell wall peptidoglycan rather than permeabilizing membranes 2. It is secreted as disulfide-linked homo- and heterodimers 2 and protects against experimental lung infection in vivo 2. Beyond direct antimicrobial effects, PGLYRP4 modulates inflammatory responses through pro- and anti-inflammatory properties independent of bactericidal activity 1. Clinically, PGLYRP4 variants show genetic association with psoriasis 3 and Parkinson's disease 4, suggesting roles in inflammatory and neuroinflammatory pathology. PGLYRP4 cooperates with other innate immune pathways to maintain gut homeostasis and protect against colitis 5, indicating broader significance in mucosal immunity and microbiome regulation.