The complement anaphylatoxin C3a, on binding the C3aR, mediates numerous proinflammatory activities. In addition, recent in vitro studies with C3a have implicated C3aR as a possible anti-inflammatory receptor. Because of its possible dual role in modulating the inflammatory response, it is uncertain whether C3aR contributes to the pathogenesis of endotoxin shock. Here, the targeted-disruption of the C3aR in mice is reported. These mice exhibit an enhanced lethality to endotoxin shock with a pronounced gene dosage effect. In addition, the plasma concentration of IL-1β was significantly elevated in the C3aR−/− mice compared with their littermates following LPS challenge. These findings demonstrate an important protective role for the C3aR in endotoxin shock and indicate that, in addition to its traditionally accepted functions in mediating inflammation, the C3aR also acts in vivo as an anti-inflammatory receptor by attenuating LPS-induced proinflammatory cytokine production.

Carboxypeptidase N (CPN) is a plasma zinc metalloprotease comprised of two small subunits that have enzymatic activity, and two large subunits, which protect the enzyme from degradation. CPN cleaves the carboxyl-terminal amino acids arginine and lysine from biologically active peptides such as complement anaphylatoxins, kinins, and fibrinopeptides. To delineate the murine CPN small subunit coding region, gene structure, and chromosome location, cDNA and genomic clones were isolated, characterized, and used in Northern and fluorescence in situ hybridization analyses. The results from this study demonstrate that the murine CPN small subunit gene is a single copy gene of ∼29 kb that is transcribed in the liver into a 1793-bp mRNA with an open reading frame of 1371 nucleotides encoding 457 aa. The gene contains nine exons ranging in size from 455 bp (exon 1) to 100 bp (exon 7), and eight introns ranging in size from 6.2 kb (intron 2) to 1.4 kb (intron 4). All intron/exon junctions follow the normal consensus rule. The mouse CPN small subunit gene localized to chromosomal band 19D2, which is syntenic to human chromosome 10q23–25. Primer extension experiments using mouse liver mRNA indicate one major transcriptional initiation site and three minor sites. Sequence analysis of the 5′-flanking region indicated a TATA-less promoter and numerous transcription factor binding sites, which may confer liver-specific expression of the CPN small subunit gene.

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