Immunostaining for markers of chondrocyte hypertrophy. Immunostaining for markers of chondrocyte hypertrophy was performed in articular cartilage sections from FM animals. Sections were probed with (a) anti-MMP-13, (b) anti-alkaline phosphatase, or (c) anti-type X collagen primary antibodies, followed by secondary antibodies conjugated to horseradish peroxidase. Colourimetric detection of each protein (brown precipitate) was carried out for equal time periods for all sections probed with the same primary antibody. Nuclei are counterstained with hematoxylin (blue). In the top row of each panel, representative sections from all time points following surgery in ipsilateral knee joints are shown. In the bottom row of each panel, representative sections from sham and contralateral knee joints at 8 and 20 weeks after surgery are shown. As a positive control, sections containing the growth plate are shown in each panel to demonstrate the expression of each protein in hypertrophic chondrocytes. Articular chondrocytes with a hypertrophic-like morphology are also indicated (arrows). Experiments for each protein were carried out on sections from at least three different animals with reproducible results. All images are shown at the same magnification, as indicated by the scale bars. FM, forced mobilization; MMP, matrix metalloproteinase.