Replication of Yersinia pestis in interferon γ-activated macrophages requires ripA , a gene encoded in the pigmentation locus

doi:10.1073/pnas.0502849102

Replication of Yersinia pestis in interferon γ-activated macrophages requires ripA, a gene encoded in the pigmentation locus

^*Department of Molecular Genetics and Microbiology and Center for Infectious Diseases, State University of New York, Stony Brook, NY 11794-5222; and ^†Department of Microbiology, Immunology, and Molecular Genetics, University of Kentucky, Lexington, KY 40536-0298

Edited by John J. Mekalanos, Harvard Medical School, Boston, MA, and approved July 13, 2005 (received for review April 6, 2005)

Abstract

Yersinia pestis is a facultative intracellular bacterial pathogen that can replicate in macrophages. Little is known about the mechanism by which Y. pestis replicates in macrophages, and macrophage defense mechanisms important for limiting intracellular survival of Y. pestis have not been characterized. In this work, we investigated the ability of Y. pestis to replicate in primary murine macrophages that were activated with IFN-γ. Y. pestis was able to replicate in macrophages that were activated with IFN-γ after infection (postactivated). A region of chromosomal DNA known as the pigmentation (pgm) locus was required for replication in postactivated macrophages, and this replication was associated with reduced nitric oxide (NO) levels but not with reduced inducible NO synthase (iNOS) expression. Y. pestis Δpgm replicated in iNOS^-/- macrophages that were postactivated with IFN-γ, suggesting that killing of Δpgm Y. pestis is NO-dependent. A specific genetic locus within pgm, which shares similarity to a pathogenicity island in Salmonella, was shown to be required for replication of Y. pestis and restriction of NO levels in postactivated macrophages. These data demonstrate that intracellular Y. pestis can evade killing by macrophages that are exposed to IFN-γ and identify a potential virulence gene encoded in the pgm locus that is required for this activity.

Footnotes

↵ ‡ To whom correspondence should be addressed. E-mail: jbliska{at}ms.cc.sunysb.edu.
Author contributions: C.P. and J.B.B. designed research; C.P. performed research; J.P.G. and R.D.P. contributed new reagents/analytic tools; C.P. and J.B.B. analyzed data; and C.P., R.D.P., and J.B.B. wrote the paper.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: Ybt, yersiniabactin; HPI, high pathogenicity island; pgm locus, pigmentation locus; iNOS, inducible NO synthase; cfu, colony-forming unit(s); BMM, bone marrow macrophage; SPI6, Salmonella enterica serovar enteritidis pathogenicity island 6.