Precursor frequency of human T4 cells responding to stimulation through the CD3 molecular complex: Role of various cytokines in promoting growth and IL2 production

Abstract

The frequency of human T4 cells induced to grow and produce IL2 in response to the anti-CD3 mAb, 64.1, was examined. T4 cells were cultured at limiting dilution and stimulated with either soluble or immobilized 64.1 in the presence of various cytokines and/or irradiated B lymphoblastoid cells as accessory cells (AC). The frequency of responding cells was assessed by examining wells microscopically for visible growth and supernatants for IL2. Immobilized, but not soluble, 64.1 was able to induce T4 cells to grow in the complete absence of AC, but only when exogenous cytokines were present. IL2 was most effective at supporting T4 cell growth in this system, with a mean of 26.0 ± 3.8% of immobilized 64.1-activated T4 cells generating a colony in cultures supplemented with IL2. IL4 could also support the growth of immobilized 64.1-activated T4 cells, but the frequency of responding cells was much lower (3.7 ± 0.9%). The combination of IL2 and IL4 was not more effective than IL2 alone. TNFα, IL1β, and IL6 were unable to support T4 cell growth alone, but each increased the frequency of T4 cells responding in the presence of IL2. AC could support the growth of a small number of 64.1-stimulated T4 cells in the absence of exogenous IL2 and enhanced the frequency of T4 cells responding to immobilized 64.1 in the presence of IL2. The percentage of immobilized 64.1-stimulated T4 cells producing IL2 was also examined. Immobilized 64.1 stimulated less than 1.4 in 1000 T4 cells to produce IL2 in the absence of AC and neither IL4 nor TNFα enhanced this response. Fixed AC and IL1β, on the other hand, caused a small increase in the frequency of immobilized 64.1-activated T4 cells that secreted IL2. The frequency of T4 cells stimulated to produce IL2 by immobilized 64.1 was greatly enhanced by the addition of AC. The data indicate that in the absence of AC, a stimulatory matrix of immobilized 64.1 is sufficient for some T4 cells to be activated to become IL2 or IL4 responsive and for a smaller percentage to secrete IL2. Additional T4 cells require IL1β, TNFα, IL6, or AC to become IL2 responsive, whereas only IL1β and AC can promote IL2 production. In the presence of AC, the amount of cytokine produced endogenously appears to be sufficient to sustain the growth of some T4 cells. These experiments, thus, have defined the conditions required to induce the growth of T4 cells stimulated by mAb to the CD3 molecular Complex.