Axial sections of the L4/L5 lumbar disks showing immunohistochemical staining with Safranin O, toluidine blue (nine weeks after surgery) and CD11b. (A) Safranin O-stained sections of sham control (left) and disk injury (right). (B) Toluidine blue-stained sections of sham control (top left) and traumatic disk puncture (top right) (original magnification, ×40). Lower panels show enlargements (original magnification, ×100) of boxed portions of top left and top right panels. Mast cells are indicated by dark blue staining. (C) CD11b-stained sections (original magnification, ×40). Immune cells are shown in dark blue staining. AF = annulus fibrosus; NP = nucleus pulposus.