Antiviral Antibodies Are Necessary for Control of Simian Immunodeficiency Virus Replication (cid:1)

To better define the role of B cells in the control of pathogenic simian immunodeficiency virus (SIV) replication, six rhesus monkeys were depleted of B cells by intravenous infusion of rituximab (anti-CD20) 28 days and 7 days before intravaginal SIVmac239 inoculation and every 21 days thereafter until AIDS developed. Although the blood and tissues were similarly depleted of B cells, anti-SIV immunoglobulin G (IgG) antibody responses were completely blocked in only three of the six animals. In all six animals, levels of viral RNA (vRNA) in plasma peaked at 2 weeks and declined by 4 weeks postinoculation (PI). However, the three animals prevented from making an anti-SIV antibody response had significantly higher plasma vRNA levels through 12 weeks PI ( P (cid:1) 0.012). The remaining three B-cell-depleted animals made moderate anti-SIV IgG antibody responses, maintained moderate plasma SIV loads, and showed an expected rate of disease progression,