CTSS and infection: While the most significant results occurred at day 3 post-infection for the inactivation of the three cathepsins, we observed a significant increase in MTB survival (P < 0.05) throughout the entire infection (Fig. 3B middle panel) in macrophages deficient for cathepsin S. Moreover, we performed flow cytometry analysis to determine if the differences observed were due to an increase of the internalization of bacteria and not due to increased survival.