CTSB and neoplasm: Therefore, it is of great interest that cathepsin B, a lysosomal cysteine protease that is found in most cell types but is most abundant in macrophages (264) and upregulated in tumor cells and TAMs (265, 266), is able to remove the amino acid cysteine from proteins (264, 267) and that bacteria that infect macrophages intracellularly are able to regulate the amount of cathepsin B produced by the infected macrophages and are able to affect the trafficking of cathepsin B (264).