The pre-BCR, GAL1, and pre-B-cell integrins relocalize in the synapse formed between normal large pre-BII cells and stromal cells. (A) Normal murine BM pre-BII cells (B220⁺CD19⁺CD117⁻Igκ/λ⁻ large forward scatter) were cocultured on OP9 stromal cells and fixed before staining. (Left) Representative view of cocultures stained with an anti-IgM Ab. Red and white stars indicate cells with relocalized and nonrelocalized pre-BCR, respectively. (Right) Cocultures were stained with the SL156 anti–pre-BCR Ab (green) and anti-GAL1 AS (red). (B) Costaining of cocultures using antibodies specific for GAL1, IgM, and CD24 and α4, β1, αL, and β2 integrins (63×/1.4 NA oil objective). (C) Western blot analysis of GAL1 expression by the BM B-cell subpopulations revealed by anti-GAL1 AS and anti–β-actin mAb.