Fig. 3

TgA86 axial pathology progresses through sequential stages of inflammation, bone erosion, and ectopic new bone formation. a Representative H&E-stained sections of the tail vertebrae show enthesitis with inflammatory cell accumulation at the periphery of the intervertebral disks (black arrows) of TgA86 mice, while representative TRAP-stained tail vertebrae show the accumulation of active osteoclasts at the sites of inflammation (black arrowheads). b Representative Safranin O-stained sections of tail vertebra show fibrocartilage formation at sites of enthesis in 20-week-old TgA86 mice and ectopic chondrocytes in 40-week-old TgA86 mice (black asterisk in higher magnification panels). c Inflammation is depicted as the percentage of vertebrae with low, intermediate, or high scores. An increase in the percentage of joints with high inflammation is observed at 20-week-old TgA86 mice and this percentage decreases by 40 weeks of age. Similarly, there is an increase in the number of osteoclasts at 20 weeks of age that drops by 40 weeks of age. d Safranin O staining of tail vertebra sections indicates increased presence of fibrocartilage (20 weeks) and of ectopic chondrocytes at later stages, 30 and 40 weeks of age. e Representative H&E-stained sections show inflammatory infiltrates accumulation in the sacroiliac joints of TgA86 mice (black arrowheads)