CLASSIFICATION OF ACTIVATION ANTIBODIES AGAINST INTEGRIN BETA-1 CHAIN

We compared the effects of two anti-beta 1 integrin activating antibod ies, TS2/16 and AG89, on K562 cell adhesion to fibronectin. Though bot h antibodies effectively induced cell adhesion, the EC50 for AG89 was more than 200-fold higher than that for TS2/16, Scatchard analysis of the data from [I-125]Fab fragment binding to the cells revealed that t he TS2/16 epitope is exposed constitutively on all the beta 1 integrin molecules, while only 3% of the beta 1 integrins on resting K562 cell s bear the AG89 epitope. Calculation of the actual number of each anti body bound to the cell during the cell adhesion assay revealed that in duction of cell adhesion can be accomplished by binding much fewer AG8 9 molecules compared to TS2/16. Thus, AG89 and TS2/16 represent distin ct classes of anti-integrin activating antibodies that show completely different binding characteristics as well as different activation eff ects on the integrin molecule upon binding. (C) 1997 Federation of Eur opean Biochemical Societies.