CTSG and acute monocytic leukemia: When exogenous CatG is introduced, this protease leads to an increase in the expression of cell surface MHC I molecules on peripheral blood mononuclear cells (PBMCs), the human acute monocytic leukemia cell line (THP-1), and human glioblastoma cells, which are further upregulated by lactoferrin-enhanced CatG activity, specifically for a B cell line [3].