CD2 and infection: To assess the effect of exposure to PM from different seasons and each size fraction on the cell viability, PBMC were exposed to 0, 0.1, 1 and 10 μg/ml of R2.5, CD2.5, WD2.5, R10, CD10 or WD10 for 20 h followed by infection with M. tb MOI1 or left uninfected for an additional 20h, and LDH leakage, as a measure of cytotoxicity, assessed.