Functional characterization of peripheral blood mononuclear cells from patients with sepsis. Peripheral blood was collected at enrollment and again seven days later from patients with severe sepsis and from normal controls. Peripheral blood mononuclear cells (PBMCs) were isolated and stimulated with α-CD3 and α-CD28 antibodies for five hours (panel A) or 48 hours (panel B) and analyzed for IFNγ secretion. A duplicate plate of PBMCs was rested overnight in fresh media prior to stimulation with α-CD3 and α-CD28 antibodies (panel C). Proliferation was determined by tritiated thymidine incorporation on PBMCs obtained at enrollment and at the end of study participation and stimulated for 48 hours with α-CD3 and α-CD28 antibodies (panel D). P values were calculated by a non-parametric 2-tailed Mann Whitney U-test (panels A and B) or a 2-tailed paired Students T-test (panel C).