Innate nonself immune recognition relies on structures common among invading microbes, a process termed pattern recognition. Peptidoglycan is a fundamental component of the bacterial cell wall and is thus a candidate for a pattern recognized by the immune system. Using differential display to identify bacteria-induced genes in the moth Trichoplusia ni, Kang et al. (1998) cloned a cDNA encoding the T. ni peptidoglycan recognition protein (PGRP, or PGLYRP). Recombinant T. ni PGLYRP bound to peptidoglycan and to gram-positive bacteria. By PCR of human and mouse spleen cDNAs, they isolated human and mouse PGLYRP cDNAs, respectively. The deduced human PGLYRP protein has 196 amino acids. Both the human and mouse PGLYRP proteins share 43% sequence identity with the T. ni PGLYRP protein. Recombinant mouse Pglyrp protein expressed in insect cells possessed an affinity for peptidoglycan. Dot blot analysis of a number of human tissue mRNAs detected strong expression in bone marrow and weak expression in lung, kidney, liver, small intestine, spleen, thymus, peripheral leukocyte, and fetal spleen. Liu et al. (2001) cloned PGLYRP, which they called PGRPS, by PCR of a bone marrow cDNA library. The deduced 196-amino acid protein contains an N-terminal signal peptide, followed by the extracellular PGRP domains III, II, and I, which are highly conserved in mammalian and insect PGRPs. PGRPS shares 40%, 43%, and 42% amino acid identity with PGRPL (608199), PGRPI-alpha (PGLYRP3; 608197), and PGRPI-beta (PGLYRP4; 608198). RNA dot blot analysis detected strong PGRPS expression in bone marrow and expression that was 50 to 100 times lower in polymorphonuclear leukocytes and fetal liver. Northern blot analysis detected 1.4-, 0.9-, and 0.5-kb transcripts in bone marrow, a 0.9-kb transcript in fetal liver, and 1.4- and 0.9-kb transcripts in peripheral blood leukocytes. PCR detected low expression of PGRPS in spleen, jejunum, and thymus, possibly due to the presence of polymorphonuclear leukocytes in these tissues. Transiently transfected COS-7 and human embryonic kidney cells expressed PGRPS as a protein with an apparent molecular mass of 24 kD. About half of the expressed PGRPS was detected in the culture medium, and the remainder was a Triton X-100-soluble membrane protein.