Fig. 6

Pathological changes of lumbar vertebrae. A Histopathologic evaluation of the ankylosed intervertebral joints. The spines from 6- to 10-year-old normal and diseased animals (n = 3) were harvested, fixed, and stained. The bone is stained blue while the cartilage, and annulus fibrosus are stained red. Representative safranin-O/fast green images of normal animals’ joint demonstrating normal joint cavity, healthy cartilage, and annulus fibrosus. Representative safranin-O/fast green images of diseased animals intervertebral joints demonstrating cartilage disruption of the disc by a heterotopic ossification tissue (magnification of the boxed area in erosion vertebrae showed bony invasion and cartilage damage). Heterotopic bone formation was shown at the edge of the vertebral bodies. The area inside the yellow dotted line was syndesmophytes, which corresponds to the place pointed by the yellow arrow on the X-ray image. The intervertebral disc of the AS cynomolgus became narrower as the disease progress until the final disappearance when cartilage fused. Representative safranin-O/fast green of diseased animals syndesmophyte demonstrating heterotopic bone, fibrocartilage (a), osteoclasts (b black arrows) and cartilage calcifications (c). FC fibrocartilage, F fibrous tissue, HB heterotopic Bone, C cartilage plate. Black scale bar = 1mm. Yellow scale bar = 100μm. B a Representative hematoxylin-eosin (HE) staining images of normal animals joint demonstrating normal anterior ligament. b Representative HE staining images of AS animals joint demonstrating anterior ligament. c Thickening of the anterior ligament. d Representative HE staining images of AS animals joint demonstrating granulation tissue (GT). There were a large amount of small blood vessels in this GT. e An amount of small blood vessels in the bone marrow (BM). f The number of vessels in the bone marrow. g An amount of inflammatory cell infiltration in the articular capsule. h There were an amount of small blood vessels in fibrous tissue (F) of the ligament. i The number of vessels in the ligament. p values calculated by Student’s t test, where *p < 0.05, compared with control (control: n=7, AS: n=12). Black scale bar = 1mm. Yellow scale bar = 100μm.