Increased SAPK activity after CD22 ligation on primary B cells and several B-cell lines. (A) SAPK kinase assays performed with lysates obtained after stimulating primary human tonsillar B cells (2 × 10⁷/lane) with media, immobilized CD22 MoAb HB22.7 (20 μg/mL), F(ab′)₂ fragments of goat MoAb to BCR (20 μg/mL), or both. Immune complex kinase assays were performed using GST-c-Jun as a substrate. (B) SAPK kinase assays performed as described in (A) after stimulation of the B-cell line Ramos (10⁷/lane) with HB22.7 (20 μg/mL), CD40 (2 μg/mL), or CD3 (10 μg/mL). (C) SAPK kinase assays performed as described in (A) after stimulation of the B-cell line HS Sultan (10⁷/lane) with the CD22 MoAbs HB22.7 and HB22.23 (20 μg/mL) or CD40 (2 μg/mL).