Target cells are lysed in the presence of serum and rituximab irrespective of presence of effector cells. Raji cells were incubated for 20 hours in media, 50% serum, or 50% serum plus PBMCs with varying concentrations of rituximab. The percent of viable target cells were determined using flow cytometry by counting annexin V and propidium iodide–negative target cells (n = 3). Error bars represent SD of the mean.