YERSINIA-PESTIS PH-6 ANTIGEN FORMS FIMBRIAE AND IS INDUCED BY INTRACELLULAR ASSOCIATION WITH MACROPHAGES

Ability to express pH 6 antigen (Ag) is necessary for full virulence o f Yersinia pestis; however, the function of the Ag in pathogenesis rem ains unclear. We determined the nucleotide sequence of a 4232 bp regio n of Y. pestis DNA which encoded the pH 6 Ag structural gene (psaA) an d accessory loci necessary for Ag synthesis. Protein sequences encoded by the Y. pestis DNA were similar to accessory proteins which functio n in the biosynthesis of Escherichia coli fimbriae Pap, K88, K99 and C S3 as well as the molecular chaperone for the Y. pestis capsule protei n. Electron microscopy and immunogold labelling studies revealed that pH 6 Ag expressing E. coli or Yersinia produced flexible 'fibrillar' o rganelles composed of individual linear strands, multiple strand bundl es or wiry aggregates of PsaA. Y. pestis associated with the murine ma crophage-like cell line, RAW264.7, expressed pH 6 Ag in an intracellul ar acidification-dependent manner. Together with an earlier study show ing that a Y. pestis psaA mutant was reduced in virulence, these resul ts demonstrate that the expression of fimbriae which are induced in ho st macrophages is involved in plague pathogenesis.