Increased inflammatory and degenerative changes in transgenic hCD2-ΔkTβRII mice after the induction of CIA. Representative sagittal histological sections stained with hematoxylin and eosin are shown. (a–c) A small joint of the extremities (a) of a wild-type mouse, and a larger joint (b), show a smooth cartilage surface without any cartilage or bone destruction. (c) The synovial lining layer is composed of flat synovial cells or is mildly hyperplastic. (d–f) Joints of transgenic mice with severe inflammatory changes also affecting the periarticular soft tissue are shown. (d) Destruction was seen in small joints, with fibroproliferative tissue (lower portion) and numerous neutrophils within the articular space (upper portion and f). Bone destruction has resulted in bone modulation. (e) In larger joints of the extremities, also, there is heavy proliferation of fibrocellular tissue (pannus formation) with joint destruction. Scale bars represent 100 μm.