Enhanced activation of CD83-positive T cells.

CD83 is a marker molecule for mature dendritic cells (DCs) but is also substantially expressed on activated T cells in humans and mice. Its function is unknown, but CD83 knockout mice show an impaired thymic maturation of CD4-positive cells and soluble CD83 inhibits partially antigen-specific responses in vitro pointing to a role of CD83 in the immune system. Here we show that CD83-positive T cells produce strongly increased amounts of interferon-gamma and interleukin-2. In contrast, constitutive expression of CD83 on DCs alters neither the activation of DCs following addition of lipopolysaccharide nor the ability to present antigenic peptides. Thus, the expression of CD83 on T cells has direct functional consequences for tuning the activation threshold.