Interaction of interleukin 2 with cells: quantitative analysis of effects.

The response of T lymphocytes to interleukin 2 (IL 2) is accurately described by a four-parameter logistic function. Both data generated by a theoretical model of IL 2-driven proliferation and experimental data conformed to this function for all doses of IL 2. Assays measuring either the rate of DNA synthesis or cellular metabolism were well described. The variance of response was not constant but increased in a predictable way. Weighting was therefore included in deriving a nonlinear curve-fitting program. The effects on response of cell density, time, and the T lymphocyte line used were examined. Assays gave reproducible estimates of potency when test preparations were compared with a standard preparation, but not otherwise. A model for IL 2 proliferation was derived on the basis of the two-state model of the cell cycle, with cells leaving a quiescent state randomly and then traversing the other stages of the cell cycle in a determinate way.