CTSS and infection: A comparative study using a pathogenic strain M. tuberculosis and a non-pathogenic strain M. smegmatis revealed that following infection with M. tuberculosis, mRNAs for the majority of CTSs were downregulated in human primary macrophages (CTSB, C, D, E, G, K, O, S, V, and W), in contrast to the non-pathogenic M. smegmatis that induced the upregulation of most CTSs. Such a global downregulation of CTSs expression decreased pathogen killing and improved intracellular bacterial survival [45].