CD69 and Huntington disease: Disturbances in the acquired response are also observed; CD4+ T lymphocytes of HD patients are characterized by a reduced expression of key surface antigens (especially co-stimulatory CD28 and activation markers: CD69 and CD25) and impaired proliferation parameters (including reduced number of cell divisions, longer period of time required by these cells to enter the first (G1) phase of the first cell cycle and decreased percentage of cells able to divide) in response to polyclonal stimulation of the TCR/CD3 complex10,11.