FIGURE 1.

Human lymphocytes show higher levels of proliferation in response to stimulation compared with chimpanzee lymphocytes, regardless of method of stimulation. PBMCs were labeled with CFSE and stimulated for 5 d with varying amounts of three different isotypes of anti-CD3 IgG Abs, combinedwithanti-CD28 costimulation (0.01 μg/ml, clone CD28.2). A, Light scatter flow cytometry plots showing percentage of activated lymphocytes (determined by size). Top panels, human cells. Bottom panels, chimpanzee cells. B, The CFSE content in each culture was analyzed by flow cytometry. All plots shown represent analysis by gating on live lymphocytes, including both resting and blasting cells, as shown in A. One experiment, representative of at least three comparisons for each Ab isotype, is shown. C, Graph summarizing data from comparisons of PBMCs that were labeled with CFSE and stimulated with: 5–10 ng/ml anti-CD3 Ab with anti-CD28 costimulation (0.1 μg/ml), 2 μg/ml PHA, and 0.5–2 μg/ml anti-CD28 superagonist ANC28.1/5D10. The CFSE content in each culture was analyzed by flow cytometry 5 d after stimulation, and the percent age of live cells with more than one cell division was determined using FlowJo software. Errors bar represent SEM. D, MLRs. Target cells are treated with mytomycin C to prevent cell division and mixed with CFSE-labeled responder cells. The percentage of activated cells was determined by flow cytometry after 7 d. Error bars represent SD. The number of experiments shown represents comparisons between cells from different individuals.