The requirement of tumour necrosis factor-alpha and interferon-gamma for the expression of protective immunity to secondary murine tularaemia depends on the size of the challenge inoculum

Tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma are necessary for immunity against secondary murine tularaemia and the extent of their requirement depends on the size of the inoculum. Non-immune mice have no defense against Francisella tularensis when treated with neutralizing monoclonal antibodies (mAbs) against TNF-alpha and IFN-gamma. Introduction of an F. tularensis inoculum of 500 c.f.u. produces infection in the livers, spleens and lungs of these mice. Immune mice treated with TNF-alpha or IFN-gamma mAbs fight secondary infection even with 50-fold larger inocula.