PBMC from IGRA- (n = 8 for M.tb and n = 6 for PPD) or IGRA+ (n = 7 for M.tb, n = 7 for PPD) subjects were exposed to 0 (no PM), 0.1, 1 and 10 μg/ml of R2.5, CD2.5, WD2.5, R10, CD10, or WD10 at 37ºC, 5% CO2 in a humidified environment for 20 h. Following exposure to PM, PBMC were infected with M.tb at MOI1 (A, B, C, D) or stimulated with PPD (E, F, G, H) and incubated for an additional 20 h. Frequencies of IFN-γ-producing PBMC were examined by ELISPOT assays. Results are shown as means ± SEM. Statistical significance (p≤0.05) relative to unexposed control PBMC is shown with solid lines. Statistically significant differences between seasons are shown with dotted lines.