Stimulation of resting normal human peripheral blood mononuclear cells by fetal calf sera. Activation to an interleukin-2 responsive state.

Normal adult human peripheral blood mononuclear cells which are negative for interleukin-2 (IL-2) receptors as assessed by flow cytofluorometry, acquire IL-2 receptors and IL-2 responsiveness after culture in media supplemented with fetal calf sera. Thus, in the absence of any known external stimuli, fetal calf sera used to supplement culture media can induce the transformation of resting (G0) peripheral blood mononuclear cells to an activated (G1) state. The activated (G1) cells are able to progress through the rest of the cell cycle (S, G2, M) in the presence of IL-2. As a result, studies of human peripheral blood mononuclear cells in fetal calf serum-supplemented culture media should be interpreted with appropriate caution.