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Infection and Immunity, December 2002, p. 6567-6575, Vol. 70, No. 12
0019-9567/02/$04.00+0 DOI: 10.1128/IAI.70.12.6567-6575.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Departments of Pathology and Laboratory Medicine,1 Molecular Biology Institute, University of California, Los Angeles, California 90095,2 Santarus, Inc., San Diego, California 921303
Received 1 May 2002/ Returned for modification 2 July 2002/ Accepted 21 August 2002
Commensal bacteria have emerged as an important disease factor in human Crohn's disease (CD) and murine inflammatory bowel disease (IBD) models. We recently isolated I2, a novel gene segment of microbial origin that is associated with human CD and that encodes a T-cell superantigen. To identify the I2 microorganism, BLAST analysis was used to identify a microbial homologue, PA2885, a novel open reading frame (ORF) in the Pseudomonas aeruginosa genome. PCR and Southern analysis identified Pseudomonas fluorescens as the originating species of I2, with homologues detectable in 3 of 13 other Pseudomonas species. Genomic cloning disclosed a locus containing the full-length I2 gene (pfiT) and three other orthologous genes, including a homologue of the pbrA/pvdS iron response gene. CD4+ T-cell responses to recombinant proteins were potent for I2 and pfiT, but modest for PA2885. pfiT has several features of a virulence factor: association with an iron-response locus, restricted species distribution, and T-cell superantigen bioactivity. These findings suggest roles for pfiT and P. fluorescens in the pathogenesis of Crohn's disease.
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