IFNγ production by memory T cells in the acute phase of the response to <i>L</i>. <i>pneumophila</i> is non-cognate and can contribute to bacterial clearance.

<p>A-C. C57BL/6 mice were injected with 10⁷ gBT-I.IFNγ-YFP T cells that had been stimulated <i>in vitro</i> with antigen. After 30 days mice were infected with <i>L</i>. <i>pneumophila</i>. A. Number of T cells derived from the recipient mice (Endogenous) and gBT-I T cells in lungs at the times shown. Cells were identified using congenic markers. Mean ± SEM is shown. n ≥ 10 for all groups and pooled from 4 separate experiments. B. Flow cytometric profiles of YFP expression of gBT-I.IFNγ-YFP T cells in lung and spleen at the days shown. Indicated gates set by analysis of endogenous cells. C. Proportion of gBT-I.IFNγ-YFP T cells in lung expressing YFP on the days shown. D. Experimental design to examine the effectiveness of IFNγ produced by memory T cells in <i>L</i>. <i>pneumophila</i> clearance. See text for further details. E. Results of experiment shown in ‘D’. WT, wild type C57BL/6 mice without transfer of T cells. IFNγ^-/-, IFNγ^-/- mice without transfer of T cells. IFNγ^-/- (+gBT-I), IFNγ^-/- mice that received IFNγ-sufficient gBT-I T cells. IFNγ^-/- (+gBT-I.IFNγ^-/-), IFNγ^-/- mice that received T cells from gBT-I.IFNγ^-/- mice. CFU/lung at day 3 after infection are shown. In C and E, each symbol represents data for one mouse. C, Data pooled from 4 separate experiments. D, Data pooled from 4 separate experiments. **. P < 0.01, ***. P < 0.005.