IL-2 influences the balance between immunity and unresponsiveness in the picryl (TNP) contact sensitivity system by blocking the development or action of an Lyt-2+, I-J+ T suppressor cell.

Mice injected with antigen (picrylated spleen cells) intravenously fail to develop contact sensitivity. However, contact sensitivity occurs if these mice are injected with IL-2. This effect of IL-2 was reproduced in vitro by taking spleen cells 2 days after injecting antigen intravenously and culturing them with either 150 u/ml recombinant IL-2 for 2 days or by pulsing with 600-1200 u/ml IL-2 at 4 degrees C for 1 hr. After 2 days in culture these antigen-exposed cells transfer contact sensitivity to naive recipients in a 24-hr experiment. However, the ability of antigen-exposed cells, pulsed with IL-2, to transfer contact sensitivity is abolished when they are incubated with unpulsed antigen-exposed cells and as few as 1/16 of their number have a significant effect. This phenomenon is specific, as normal cell or cells from mice injected with oxazolonated cells intravenously have no effect. The suppressor cells were Thy-1+, Lyt-1-, 2+, I-J+ T cells. It was concluded that IL-2 prevents the development/action of antigen-specific T suppressor cells.