Effect of rituximab infusion on concentrations of CD20⁺ B cells. Changes to CD20⁺ B cells are shown in blood (A), lymph nodes (C), and intestine (D). Rituximab infusion induced a depletion of B cells and did not mask the CD20 molecule, as shown by the CD79a staining (B). Black symbols and lines denote the control monkeys (DG34, DH44, DD93, and BV85). Red symbols and lines denote monkeys in which rituximab administration induced complete B-cell depletion in both peripheral blood and tissues (CF03, BT49, and EI09). Green symbols and lines indicate monkeys in which rituximab induced complete peripheral but incomplete tissue B-cell depletion (DG04, CA16, and EL55). The violet dots and line indicate a RM in which B-cell depletion was achieved after every rituximab administration but B cells rebound before the following treatment. Day 0 is the day of SIV inoculation. Rituximab was infused every 21 days beginning 1 week before SIV inoculation. RMs DG04, CA16, CF03, and BT49 received 4 rituximab administrations. RMs EI74, EI09, and EL55 received rituximab for up to 160 days pi.