Transmigration assay of purified B cells. Migration of primary B cells from HIV-1–infected patients and controls toward CXCL13 (A), CXCL12 (B), and CCL21 (C) in a transmigration assay. Migration index is presented as migrated cells toward the specific chemokine divided by spontaneous migration. Migration of purified B cells toward CXCL13, CXCL12, and CCL21 is increased in HIV-1–infected patients with low CD4⁺ T-cell counts compared with healthy donors and patients with high CD4⁺ T cells.