Presence of asporin. (a) Localization of asporin in the outer annulus of the human disc. Note that there are some cells that do not show asporin localization (arrow). (b) The presence of asporin is shown in the inner annulus of the human disc; note a nearby cell without asporin content (arrow). (c) Negative control. (d) Positive control showing localization of asporin in articular chondrocytes of the rat humerus (a, b, c × 260; d × 300).