Expression of collagen type II and aggrecan in cultured human articular chondrocytes. (a) Cells were labelled with polyclonal rabbit anti-human collagen type II and secondary antibody conjugated with Alexa Fluor 594 (red). (b) Cells were labelled with monoclonal mouse anti-human aggrecan and secondary antibody conjugated with Alexa Fluor 488 (green). The nuclei were visualized by Dapi dye (blue). Isotype controls had no staining (not shown).