IVIg binding to CD22 enhances SHP-1 recruitment. (A) Tonsillar B cells were incubated with anti-IgM–coated beads in the presence or absence of IVIg for 20 minutes at 4°C and 3 minutes at 37°C before lysing the cells. Lysates were incubated with anti-CD22 and protein G-coated Sepharose beads and immunoprecipitates analyzed by WB using anti-CD22 or anti–SHP-1 Ab. Nonstimulated B cells (Unst.) are shown as control. (B) The degree of coprecipitation is presented as a ratio of intensity of SHP-1 band/intensity of CD22 band.