Oxygen-dependent patterns of collagen distribution in healthy and osteoarthritic chondrocytes. Representative images of matrix staining patterns are shown. Paraffin sections were either double-stained with anti-collagen I and anti-collagen II antibodies or single-stained with anti-collagen X as described in Materials and methods. 4′,6-diamidino-2-phenylindole was used as a counterstain for nuclei. Positive immunolocalization of collagen appears in red (collagen II) or in green (collagen I, collagen X), and nuclei are shown in blue. Negative controls with isotype-matched antibodies (images not shown) were used for background correction. Composite images of matrix staining and nuclei were digitally processed using ImageJ software (National Institutes of Health, Bethesda, MD, USA). Scale bars = 100 μm.