Lethal pulmonary infection with Francisella novicida causes depletion of αβ T cells from lungs

Respiratory Francisella infections induce a delayed innate immune response followed by a severe sepsis like condition. In this study, mice infected intranasally with Francisella novicida showed a depletion of αβ T cells in lungs while exhibiting large accumulations of other leukocytes correlating with disease severity. The depleted T cells were predominantly CD4+. The αβ T cells in infected mice showed significantly higher levels of Annexin V binding than those in mock control mice suggesting increased apoptosis of T cells. These results suggest that lack of transition from an innate to adaptive host response is associated with lethality of respiratory tularemia.