Fig. 3

Immunohistochemical localization of collagen triple helix repeat containing 1 (CTHRC1) expressing cells in arthritic synovium. Immunohistochemical staining (IHC) for CTHRC1 was positive for hypercellular pannus of the synovial joints of the hind paws (a) and of the knee (b–f) of BALB/c mice with experimentally induced arthritis. Specificity of the IHC staining was confirmed using the complete staining protocol on Cthrc1 gene-deficient mouse skeletal tissues (g). An additional control is shown using Cthrc1-wildtype tissue sections that were incubated with secondary donkey anti-rabbit antibody alone, which produced no signal (h). CTHRC1+ cells were found in the arthritic pannus intimal lining (a, e, f) and at the bone-pannus and cartilage-pannus boundaries (a–d). Dotted line shows the border between cartilage (Ct) and bone (Bn) (b). Fct fibrocartilage, Syn synovial cavity. Sections were counterstained with alcian blue (c, d, g) or with hematoxylin (a, b, e, f, h). Scale bars are 100 μm (a), 50 μm (b, c, e, g, h), and 20 μm (d, f)