The superantigenic toxin of Yersinia pseudotuberculosis: a novel virulencefactor?

Recently, a superantigenic toxin designated YPM (Yersinia pseudotuberculosi s-derived mitogen) was characterized in the supernatant of Y. pseudotubercu losis a Gram-negative bacterium involved in human enteric infection. To ass ess the role of YPM in pathophysiology of Y; pseudotuberculosis, a superant igen-deficient mutant was constructed and its virulence was tested in a mur ine model of infection and compared with the virulence of the wild-type str ain (wt). Determination of the survival rate after intravenous inoculation of mice clearly demonstrated a higher survival rate when animals were infec ted with the superantigen-deficient strain. This decreased virulence of the mutant strain could not be explained by a lower bacterial growth rate in s pleen, liver or lung of infected animals. Therefore, production of IFN gamm a, TNF alpha, IL-2, IL-6 and IL-10 was followed during the course of infect ion by cytokine assay in the blood and mRNA detection in the spleen. IL-6 a nd IFN gamma were the two major cytokines detected whereas TNF alpha produc tion was never observed.