TABLE 3.

IFN-γ production and number of IFN-γ-producing CD4⁺ and CD8⁺ lymphocytes correlated to the level of protection in the lungs

Vaccine	Amt of IFN-γa (pg/ml)	No. of IFN-γ+ T cells in lungb		Log10 resistance (CFU)c
		CD4+	CD8+
Naïve (not infected)	96	0.64	0.26	NA (NA)
Unvaccinated	96	4.63	1.61	NA (5.07 ± 0.11)
BCG	125	2.87	2.43	0.78* (4.29 ± 0.16)
Ag85B-ESAT-6	183	5.01	3.24	<0 (5.17 ± 0.09)
DDA-TDB	108	5.09	2.29	<0 (5.22 ± 0.02)
DDA-TDB-Ag85B-ESAT-6	15,180**	14.87	5.88	0.87* (4.20 ± 0.10)

^aPBMCs were assayed for IFN-γ at the peak of the response (1 week after the last vaccination). IFN-γ levels were measured in culture supernatants after 3 days of restimulation with the vaccine antigen (Ag85B-ESAT-6 [2.5 μg/ml]).

^bLymphocyte numbers represent the percentages of IFN-γ⁺ cells in CD4⁺ and CD8⁺ gated lymphocyte populations isolated from lungs 3 weeks after aerosol infection. The cells were stimulated with antigen in vitro for 72 h before flow cytometric analysis.

^cProtective efficacy of the vaccines is expressed as the log₁₀ reduction in bacterial load in the lungs compared to mice in the unimmunized group (naïve) from a minimum of four mice per group, assayed individually at 6 weeks postinfection. NA, not applicable. Values significantly different from mice in the naïve group are marked (*, P < 0.05, **, P < 0.001). Data are means ± standard errors of the means.