(a) Detection of cathepsin S activity in MSG cells and its inhibition by Clik60 (10–5 M). (b) Surface expression of class II molecule induced by IFN-γ stimulation on MSG cells was clearly inhibited by the incubation with Clik60, but not the incubation with CA074 and Clik148, as determined by flow cytometry. (c) Colocalization of FITC-labeled AFN303-318 peptide and class II (I-Aq) molecule in the IFN-γ–stimulated MSG cells. Prevention of the surface expression of peptide–class II complex formation was confirmed by the inhibition of Clik60, but not by inhibition of Clik148 and CA074.