Cytokine levels in the plasma of infected mice. Cytokines were measured from plasma samples as described in Materials and Methods. Closed symbols: IFN-γ +/+ mice, open diamonds: IFN-γ −/− mice. Values are given in pg/mL except for G-CSF levels, which are given in the lowest dilution (see basis for this assay in Materials and Methods). Data representative of multipe experiments. We consistently detect IL-6, but IL-3 and GM-CSF levels are commonly at the background level of the ELISA assay.