Memory B cells closely interact with MIP-3α– and SDF-1–expressing cells and PCs with BCA-1–producing cells.

Tonsil sections were double-stained with anti–SDF-1 (A,C) or anti–MIP-3α (B,D) Abs and anti-CD19 (A,B; blue) or anti-IgG (C,D; red) Abs. SDF-1– and MIP-3α–producing cells are shown in red in panels A and B, respectively, and in blue in panels C and D, respectively. The section in panel E was double-stained with anti-CD38 (red) and anticytokeratin-19 (blue) mAbs and the section in panel F with anti–BCA-1 (red) and anti-CD27 (blue) Abs. PCs are located as clusters at the lymphoepithelial junction of the crypts (E). This site corresponds to the sites of the crypt BCA-1 expression (F). The stainings are representative of 4 different tonsil specimens. Original magnifications are × 20 for panels A, B, and E; × 40 for panels C, D, and F. * indicates lumen of the crypt.