Ability of pure resting CD8+ human T cells to respond to alloantigen

Transient expression of human interleukin-2 and interferon-gamma genes is regulated by interaction between distinct cell subsets

The level of transient expression of human IL-2 and IFN-gamma genes, we show, is regulated by dynamic interaction between two functionally distinct cell populations. One is able to express these genes, while the other, bearing one of several specific surface markers, actively inhibits their expression. Defined cell subsets were isolated from PBMC and tonsil cells using immunomagnetic beads coated with monoclonal antibodies directed against surface markers. Depletion of CD8, CD11a (Leu15), or Leu8 subsets led to a pronounced superinduction of IL-2 and IFN-gamma gene expression when the remaining cell population was stimulated with mitogen (PHA) or antigen (SEB). Thus, a 10-fold increase in production of IFN-gamma was observed after removal of CD11a (Leu15) cells constituting only a small percentage of the total cell population. By contrast, depletion of cells expressing CD19, a B cell marker, did not yield any superinduction. Conversely, CD8, CD11a (Leu15), or Leu8 cell subsets, but not CD19 cells, each inhibited the induction of IL-2 and IFN-gamma gene expression almost completely in depleted or total cell populations from which they were derived. Gene expression occurring within one cell subset could be effectively inhibited by cells from a second subset. Introduction of inhibitory cells (Leu8) into a population that actively expressed IL-2 and IFN-gamma mRNA resulted in an immediate cessation of gene expression. This suppression involves a soluble mediator, since the culture medium in which such cells were activated exerted a similarly effective inhibition.

The potential to express or suppress human interleukin-2 and interferon-gamma genes is not restricted to distinct cell subsets

Cell surface markers CD4, CD8, Leu8 and Leu15 (CD11) were used to separate human lymphoid cell subsets with monoclonal antibody-coated immunomagnetic beads. We show that each of these subsets is able to suppress the induction of IL-2 and IFN-gamma genes effectively. This is manifested by a pronounced superinduction of IL-2 and IFN-gamma mRNA, as well as IFN-gamma protein, in cell populations depleted of one of these subsets. Co-culture of cell subsets with total cell populations or depleted ones, on the other hand, leads to severe inhibition of expression of these genes. In these experiments, cells in suppressor subsets exhibit little, if any, expression of IL-2 and IFN-gamma genes. By contrast, depending on donor and lymphoid tissue examined (tonsils or peripheral blood mononuclear cells), CD4, CD8, Leu8, and Leu15 cell subsets are also able to express IL-2 or IFN-gamma genes to high levels. Moreover, in Leu8+ cells that do not express the IFN-gamma gene, extensive expression of both mRNA and protein can be elicited by inhibiting the activation of suppressor cells with gamma-irradiation before induction. These results support the concept that the potential to express or suppress human IL-2 and IFN-gamma genes is not restricted to distinct cell subsets. Suppression or expression can be elicited in cells carrying a given surface marker, depending on the state of the immune system in a lymphoid tissue.