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Abstract Peptidoglycan recognition proteins PGRPs constitute a family of innate immune recognition molecules. In Drosophila, distinct PGRPs bind to peptidoglycans on gram-positive or gram-negative pgrp protocol and provide essential signals upstream of the Toll and Imd pathways required for immunity against infection.

In this paper, we provide direct evidence that the longest family member, PGRP-L, is a pgrp protocol serum protein with the capacity to multimerize.

Using gene targeting to create PGRP-L-deficient mice, we demonstrate little contribution by PGRP-L to systemic challenge using gram-negative bacteria Escherichia coli, slightly less susceptibleGram-positive bacteria Staphylococcus aureusor yeast Candida albicans.

Peritoneal macrophages from PGRP-L-deficient mice produced decreased pgrp protocol of the inflammatory cytokines interleukin 6 and tumor necrosis factor alpha when stimulated with E. Additionally, these cells produced similar amounts of cytokines when challenged with gram-positive or pgrp protocol peptidoglycans.

In contrast to its critical role in immunity in flies, PGRP-L is largely dispensable for mammalian immunity against bacteria and fungi.

The ability of the host to distinguish between self and nonself remains a central hallmark of innate immunity. Microbial organisms express distinct cell surface molecules, such as peptidoglycan PGN and lipoteichoic acid LTA on gram-positive bacteria and lipopolysaccharide LPS on gram-negative bacteria, that are structurally indispensable pgrp protocol of the cell wall.

Recognition of these pathogen-associated molecular patterns, or PAMPs 14is achieved predominantly by the vertebrate Toll-like receptor TLR family proteins, which collectively mediate induction of antimicrobial defensins, cytokines, chemokines, and dendritic cell maturation important to innate and adaptive immune responses.

PGN recognition proteins PGRPs were first identified by their ability to bind PGN and complement the prophenoloxidase cascade that induces melanization around pathogens in insects Thirteen PGRP family members are present in Drosophila 36and each contains a conserved carboxyl-terminal region with homology to bacterial T7 lysozyme The N-acetylmuramyl-l-alanine amidase activity may function to reduce the immunostimulatory effects of PGN Definitive evidence indicating essential roles for PGRPs in Drosophila innate immunity was revealed in studies of mutants defective in Pgrp protocol and Imd pathway-mediated antimicrobial responses.

Infection of flies by gram-positive bacteria and fungi induces localized production of cleaved Spaetzle, the Toll ligand. Infection by gram-negative bacteria results in activation of Imd, a Drosophila RIP-like adapter 5and the Relish pathway, with expression of antibacterial peptides active against these bacteria, including diptericin, attacin, drosocin, and cecropins Drosophila with a mutated PGRP-SA gene failed to activate drosomycin expression and was unable to survive challenge with gram-positive bacteria In contrast, responses to gram-negative bacteria and fungi were not affected.

The capacity of PGRP-SA to bind to PGN, likely in conjunction with gram-negative binding protein 624must therefore constitute a crucial and nonredundant recognition element upstream of Toll pathway activation in Drosophila.

Like Imd mutants, PGRP-LC mutants poorly induced antimicrobial peptides, particularly diptericin, and demonstrated increased susceptibility to gram-negative bacteria; responses to gram-positive bacteria and fungi were unaffected. Although LPS is a major component of the gram-negative bacterial cell wall, PGN constitutes a shared cell wall element in both gram-positive and gram-negative bacteria Structurally similar, these cell wall PGNs differ pgrp protocol the third amino acid of the peptide side chain, where lysine Lys-PGN and meso-diaminopimelic acid Dap-PGN are used in gram-positive and gram-negative organisms, respectively Together, these studies suggest that different PGRP proteins in Drosophila mediate direct interactions with pgrp protocol PGN moieties in bacterial cell walls as a proximal mechanism upstream of Toll and Imd activation.

Innate Immune Responses in Peptidoglycan Recognition Protein L-Deficient Mice

The remaining family members have critical amino acid substitutions that abrogate pgrp protocol activity 435but all four mammalian proteins retain the ability to bind PGN in vitro A nonpathogenic gram-positive Bacillus species was cleared less efficiently, however, and the killing and digestion of gram-positive bacteria by PGRP-SA-deficient neutrophils were compromised in vitro, although phagocytosis remained intact.

To define further the function of PGRPs in mammalian innate immunity, we disrupted the mouse PGRP-L gene and examined the role of this pgrp protocol in host defense against bacterial and fungal challenges.

Primers were used as follows: The targeting construct was linearized with NotI and was transfected into PrmCre ES cells, which express the Cre recombinase under control of the protamine promoter The neomycin resistance cassette was deleted in the male germ line by Cre-mediated recombination after breeding chimeric mice to wild-type mice.

Finally, heterozygous animals were interbred to obtain pgrp protocol mice.

Innate Immune Responses in Peptidoglycan Recognition Protein L-Deficient Mice

The following PCR conditions were used: Cell lines and transfections. They were subsequently subcloned into the pgrp protocol 3.


Two pgrp protocol of each plasmid DNA was transfected into cells plated in six-well plates by using a calcium phosphate protocol.

Cells were collected and assayed 48 h after transfection.