N-formylpeptides derive from bacterial and mitochondrial proteins, and bind to specific receptors on mammalian phagocytes. Since binding induces chemotaxis and activation of phagocytesin vitro
, it has been postulated that N-formylpeptide receptor signaling in vivo
may be important in antibacterial host defense, although direct proof has been lacking. Mice genetically deficient in formyl peptide receptor (FPR-/-) have no obvious developmental defects and do not develop spontaneous infection when derived in specific pathogen-free conditions. This suggests that, under these conditions, FPR is dispensable. However, when challenged with Listeria monocytogenes, FPR-/- mice have accelerated mortality and increased bacterial burden in liver and spleen early after infection, which suggests a role for FPR in host defense, specifically through regulation of innate immunity.
Drs. Ji-Liang Gao and Philip Murphy in the Laboratory of Molecular Immunology, NIAID, made the FPR-/- mouse by targeted gene disruption in 1999. The Fpr1
gene was mutated by replacing a 150 bp DNA fragment in the Fpr1
open reading frame with a neomycin resistance gene. The disrupted Fpr1
gene was introduced to 129/Sv ES cells to create chimeric mice, and then the chimeric founders were backcrossed to C57BL/6NAi mice for 10 generations in the NIAID barrier facility at Taconic. At this point, it was discovered that the C57BL/6NAi line had become contaminated with the IFNγ knockout gene. Line 4169 was then backcrossed to C57BL/6NTac (Taconic B6
) for 5 generations in order to eliminate the contaminating gene and put the strain onto the Taconic C57BL/6 subline background.