Age related decline in the proliferative response of human T cells to OKT3 stimulation

The level of the in vitro proliferative response of human peripheral blood mononuclear cells (PBMC) to the OKT3 monoclonal antibody is directly related to the level of monocyte representation in the cell population. The responses to OKT3 stimulation of PBMC obtained from different individual are difficult to interpret due to variable percentage representation of monocytes. To eliminate this problem purified T cells from humans of various ages were incubated with 2 ng/ml OKT3 antibody and 10% purified autologous monocytes. The 3H-TdR incorporation of 1 x 105 T cells at 72 hrs of culture was 69,939 +/- 6085 (SEM) cpm for young individuals (mean age 35 yrs) and 33,163 +/- 2962 cpm for healthy elderly individuals (mean age 78 yrs). In addition, IL2 receptors were measured using two color fluorescence and flow cytometry with phycoerythrin conjugated anti-IL2 receptor antibody and FITC conjugated OKT11 antibody. The percentage of cells expressing IL2 receptors was 46% for the cells from the young individuals and 23% for cells from old individuals. These results suggest that the age related decline in the proliferative ability of T cells is partially due to a decreased expression of IL2 receptors and that proliferation and IL2 receptor expression is under the control of monocyte accessory cells