Transcript levels of Nos2 and production of nitric oxide by Mtb -infected BMM. (A) Total host RNA from CDC1551 or HN878- infected BMM at 6 and 24 hpi was used to quantify the levels of Nos2 mRNA levels. The expression levels were normalized to Gapdh levels from the same sample and relative fold change was calculated by comparing uninfected with 6 and 24 hpi samples. (B) Production of nitric oxide measured as dissolved nitrite (NO2-) using Griess reagent as described in methods. The culture supernatants from BMM infected with CDC1551 or HN878 were collected 24 hpi and the amount of NO2- was measured in triplicate samples per infection. Relative NO2- concentrations were calculated by extrapolation of values from test samples on standard curves generated using sodium nitrite. Data represent mean ± standard error from two independent experiments performed in triplicate for each experimental group.