**2.3 Cysteine proteinases**

This group includes the cathepsins B, H, L, and S, which have been implicated in COPD. Cathepsin S and L are potent elastases *in vitro* (5,6) and contribute to macrophage-mediated ECM degradation. Inhibitors for this group, again include the universal inhibitor, α2-M, but also the cystatin superfamily and the kininogens (32).
