CTSB and HIV-1 infection: In the present study, we found that HIV-1 infection modulates the expression, secretion and activity of cathepsin B and of its natural inhibitors, cystatins B and C. We also found that secreted bioactive cathepsin B contributes to neuronal apoptosis, which can be reversed by the addition of a specific cathepsin B inhibitor or an antibody to cathepsin B. This data suggested a dysregulation of cathepsin B compartmentalization and inhibition systems.