Note that these differences were not due to alterations in bacterial load in lung tissue, because the number of viable bacteria in lungs of C57BL/6 mice and IFNγ-/- mice at 2 days after infection was not significantly different (C57BL/6, 1.22 x 106 ± 3.45 x 105; IFNγ-/-, 1.39 x 106 ± 2.6 x 105; n = 5, NS). This evidence concerns the gene IFNG and infection.