CXCL13/CXCR5 signaling effect on B-cell activation by antigen. (A) CD86 (top panels) and CD69 (bottom panels) profiles of a representative experiment of MD4 B cells settled on membranes with tethered HEL at the specified densities alone (gray filled histogram) or with CXCL13 (black line). Dashed gray line is the isotype control; black bar, CD86^hi and CD69⁺ B cells. (B) Frequency of CD86^hi (left panel) and CD69⁺ (right panel) MD4 B cells in the same conditions as in panel A; dots represent single experiments; black horizontal bars, averaged values. All experiments were performed in the presence of ICAM-1 (150 molecules/μm²). ns indicates not significant. *P < .05; **P < .001.