Cell surface expression of CLIP and MHC class II determinants on lymphoblasts and the T47D breast cancer cell line. PHA lymphoblasts (identified by electronic gating for cell size and scatter) and the T47D cell line were assessed flow cytometrically for expression of the MHC class II determinants and for cell surface CLIP. MHC class II expression was assessed by staining the cells with murine anti–HLA-DR followed by counterstaining with FITC-conjugated sheep antimouse IgG. Control cells were pretreated with normal mouse serum before counterstaining (A, lymphoblasts; C, T47D). CLIP expression was assessed by staining with affinity-purified rabbit anti-CLIP antibody and counterstaining with FITC-conjugated goat antirabbit IgG. As controls, the lymphoblasts and the T47D cell line were pretreated with rabbit prebleed IgG before counterstaining with FITC goat antirabbit IgG (B, lymphoblasts; D, T47D breast cancer cell line).