Generation of DT40 mutant cells expressing mouse CD19.

(A) Cell-surface expression levels of mouse CD19 on various mutant DT40 cells and of endogenous CD19 on purified murine splenic B cells. Flow cytometry analysis was performed by using biotin-conjugated antimouse CD19 mAb 1D3 followed by FITC-conjugated streptavidin (solid lines). Dotted lines show staining with isotype-matched control IgG2a. (B) Expression of various signaling molecules in various mutant DT40 cells was analyzed by Western blotting using indicated Abs. (C) Cell-surface expression of BCR was analyzed using FITC-conjugated anti–chicken IgM. Unstained cells were used as negative controls (dotted line).