C-reactive protein: a predominant LPS-binding acute phase protein responsive to Pseudomonas infection

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Abstract
As a structural component of the outer membrane of Gram-negative bacteria, endotoxin, also known as lipopolysaccharide (LPS) exhibits strong immunostimulatory properties, rendering it a pivotal role in the pathogenesis of Gram-negative septicaemia. Our attempt to identify LPS-binding proteins from the hemolymph of the horseshoe crab led to the isolation and identification of C-reactive protein (CRP) as the predominant LPS-recognition protein during Pseudomonas infection. CRP is an evolutionarily ancient member of a superfamily of `pentraxins'. It is a major protein in acute phase of infection in humans. Our investigation of CRP response to Pseudomonas aeruginosa unveiled a robust innate immune system in the horseshoe crab, which displays rapid suppression of a dosage of 106 CFU of bacteria in the first hour of infection and effected complete clearance of the pathogen by 3 days. Such a high dose would have been lethal to mice. Full-length CRP cDNA was cloned. Analysis of the untranslated regions suggests their crucial role in post-transcriptional regulation of CRP transcript levels. Northern blot analysis demonstrated an acute up-regulation of CRP by about 60-fold in 6—48 h of Pseudomonas infection. Taken together, our results provide new insights into the importance of CRP as a conserved molecule for pathogen recognition.