CST4 and infection: Moreover, the expression levels of cathepsins B, C, H, O, S and L were the most differentially regulated between the two mycobacteria; in the case of cystatins, the most distinguishable were cystatins A, F and S. Interestingly, cathepsin L showed the opposite effect, being up-regulated upon infection with MTB, similarly to that observed in M0 macrophages (Fig. 1A).