Interaction of Yersinia with host cells.

The Yersinia genus contains three species that are pathogenic for humans: Y. pestis, the agent of plague, and two enteropathogens, Y. pseudotuberculosis and Y. enterocolitica, that are generally acquired by ingestion of contaminated food. While Y. pseudotuberculosis is mainly a rodent pathogen, Y. enterocolitica is a frequent cause of disease in humans and provokes gastrointestinal syndromes of variable severity. After infection, secondary manifestations such as erythema nodosum and reactive arthritis can occur (for review, see Cover and Aber, 1989). Although these three pathogens have different entry routes and cause different diseases, they share a remarkable tropism for the lymphoid tissues of their host, where they are able to resist the non-specific immune defense mechanisms.