Western blot analysis of recombinant polypeptides. (A) Cells transiently transfected with plasmids containing wild-type GP Ibα (wt), no insert (sham), the AT deletion alone (AT del), or the AT deletion in combination with the T → C mutation (AT Del + T → C) were analyzed for expression of GP Ibα with the monoclonal antibody WM-23. (B) Stable cell lines expressing the wild-type GP Ib-IX complex (αβIX cells) or a complex containing the AT-deletion mutant (α^mutβIX) were analyzed for GP Ibα expression in the cells and in the cell supernatant (medium).