IL21 and infection: As shown in Figure 2A (individual animals) and 2B (mean±SEM for the two experimental groups), following experimental infection with SIVmac239 both groups of RMs experienced a rapid, exponential increase in virus replication that peaked before initiation of IL-21 treatment (at approximately day 14 p.i.)in four out of six IL-21-treated and three out of six control monkeys.