IVIg modulate BCR-associated signaling pathways. Phosphorylation levels of CD22, CD19, Lyn, BLNK and PLCγ2 were determined by FACS. (A) Tonsillar B-cell subpopulations were incubated with or without 20 mg/mL IVIg or 1 mg/mL IVIg SA+ or 20 mg/mL IVIg SA− for 20 minutes at 4°C and warmed up for 3 minutes at 37°C without any stimulation. B cells were subsequently fixed with p-formaldehyde, permeabilized and then stained with rabbit anti–phospho-CD22, anti-phosphoCD19, and anti–phospho-Lyn and developed by FITC–donkey anti–rabbit Ig Ab, and with PE-conjugated anti–phospho-BLNK and anti–phospho-PLCγ2. (B) Tonsillar B cells were stimulated with anti-IgM Ab–coated beads for 3 minutes at 37°C in the presence or absence of 20 mg/mL IVIG, 1 mg/mL IVIg SA+ or 20 mg/mL IVIg SA− for 20 minutes at 4°C. Activated B cells were stained with anti–phospho-CD22, anti–phospho-CD19, anti–phospho-Lyn, anti–phospho-BLNK and anti–phospho-PLCγ2 with the same protocol as before. The results represent mean percentages ± SD of 3 independent experiments. Statistical analyses were performed using the 2-tailed paired Student t test. *P < .001 vs cells incubated with no IVIg.