Peptidoglycan recognition proteins (PGRPs or PGLYRPs) are innate immunity molecules that contain a conserved peptidoglycan-binding type 2 amidase domain that is homologous to bacteriophage and bacterial type 2 amidases (Kang D et al. 1998; Liu C et al. 2001; Royet J and Dziarski R 2007; Royet J et al. 2011; Dziarski R et al. 2016). Mammals have a family of four PGRPs (PGLYRP1, 2, 3 & 4) that are differentially expressed in a cell-type or tissue-specific manner. PGLYRP2 (also known as PGRP-L) is constitutively produced in the liver and secreted into the blood (Liu C et al. 2001; Zhang Y et al. 2005; De Pauw P et al. 1995; Hoijer MA et al. 1996). PGLYRP2 expression can also be induced in the skin and intestine upon exposure to bacteria or pro-inflammatory cytokines (Wang H et al. 2005; Li X et al. 2006). Constitutive and inducible expression of PGLYRP2 in the liver and skin respectively required different transcription factors (Li X et al. 2006). PGLYRP2 is a (Zn2+)-dependent N-acetylmuramoyl-L-alanine amidase that hydrolyzes the amide bond between the MurNAc and L-alanine in bacterial cell wall peptidoglycan (Wang ZM et al. 2003; Zhang Y et al. 2005). The minimal peptidoglycan fragment hydrolyzed by PGLYRP2 is MurNAc-tripeptide (Wang ZM et al. 2003). Due to its amidase activity, human PGLYRP2 is thought to reduce inflammatory properties of bacterial peptidoglycan by cleaving it into biologically inactive fragments (Hoijer MA et al. 1997; Wang ZM et al. 2003; Royet J and Dziarski R 2007).