Fig. 1. Frozen sections (A,B) and isolated chondrocytes (C-F) from 7-day bovine articular cartilage immunolabelled for 5 (A,C,E) and ß1 (B,D,F) integrin subunits. 5 and ß1 integrin subunits are localised throughout the depth of the articular cartilage (A,B) although not every chondrocyte is labelled. Isolated chondrocytes from surface zone immediately after sequential pronase/collagenase isolation labelled with antibody to alpha 5 (C) and ß1 (D) subunits. Labelling for 5 (E) and ß1 (F) is also present 72 hours after differential adhesion to fibronectin. Fibronectin-EDA was localised in frozen tissue sections to the surface 2-3 cell layers (G). Integrin 5 and ß1 subunit expression was assessed by flow cytometry after sequential pronase/collagenase digestion (4 hours) and 72 hours after differential adhesion assay to fibronectin (H). At 4 hours and 72 hours, there was no difference in integrin subunit expression between surface zone chondrocytes (P>0.05), although during this time period the overall expression of 5 and ß1 subunits was significantly decreased (P<0.01). At 4 hours, middle zone chondrocytes had a higher expression of ß5 subunits relative to ß1 subunits (P<0.01), although there was no difference in expression after 72 hours (P>0.05).