Representative images showing immunohistochemical localization of cathepsin K in the human disc. Immunohistochemical localization (black localization product) shows the presence of cathepsin K in the outer annulus (Figure 4A). Figure 4B shows an adjacent negative control section from the outer annulus. Within the inner annulus (Figure 4C) and nucleus (Figure 4D), both positive and negative cells were present. (Scale bar for Figure 4A is the same as that shown for Figure 4B).