Cytokeratin 8 (CK8) and vimentin expression in bovine and porcine disc cells. Dual immunofluorescence staining of CK8 and vimentin (VIM) performed on freshly isolated bovine nucleus pulposus cells (a-c), bovine annulus fibrosus cells (d-f), and porcine notochordal cells (g-i). Nuclei were visualized with DAPI (4'-6-diamidino-2-phenylindole) (scale bar = 60 μm). All cells examined were positive for VIM (b,e,h). No annulus cells were positive for CK8 (d). Some bovine nucleus cells -- forming clusters, as indicated by an arrowhead in (a) -- and all porcine cells (g) were positive for CK8; these cells co-expressed VIM (c,i).