Following BCR Stimulation, Phosphorylated Igα Is Retained on the Cell Surface

<p>(A) A20IIA1.6 cells were surface-biotinylated with Sulfo-NHS-SS-Biotin on ice, stimulated with anti-IgG for the indicated times (min) and then biotin was stripped from the cell surface. Lysed samples were precipitated sequentially with streptavidin and then anti-Igα antibodies. Parallel samples were then immunoblotted with anti-phosphotyrosine (4G10) or anti-Igα antibodies. (B) Cells were labeled and stimulated as above except that biotin was not stripped from the cell surface. Streptavidin precipitations were then sequentially immunoblotted with 4G10 and anti-Igα antibodies. (C) Resting surface-biotinylated cells were directly lysed and sequentially precipitated with streptavidin and then anti-Igα antibodies. Precipitations were Western blotted with anti-Igα antibodies.