A superantigen as virulence factor in an acute bacterial infection

This study addresses the role of a bacterial superantigen as a potential virulence factor during an acute systemic infection. BALB/c mice were intravenously infected with a recombinant Staphylococcus aureus strain capable of producing plasmid-encoded staphylococcal enterotoxin B (SEB) or with the SEB plasmid-deficient parental strain. Infection with SEB-producing bacteria resulted in an initial expansion and subsequent decrease of circulating V beta 8+ T lymphocytes. This numeric decrease was accompanied by a SEB-specific state of hyporesponsiveness of splenic T cells. In parallel with SEB-triggered unresponsiveness of a large proportion of T lymphocytes, a weakening of the overall T cell responsiveness towards the invading bacteria was found. Furthermore, the production of SEB altered the kinetics of bacterial clearance: Animals infected with the SEB-producing variant showed a significantly elevated bacterial burden and could less efficiently clear the bacteria. However, the overall effect of SEB production on the course of bacterial infection was surprisingly weak, suggesting that the superantigen was only a minor virulence factor for the bacterium.