Activation of CD8(+) T lymphocytes through the T cell receptor turns on CD4 gene expression: Implications for HIV pathogenesis

T cell activation through the T cell receptor is necessary to achieve a specific and effective immune response. We report here that stimulation of CD8(+) T cells through the T cell receptor complex leads to de novo expression of the CD4 antigen on the cell surface that results in susceptibility of CD8(+) T cells to HIV infection. In addition, activation of peripheral blood mononuclear cells from HIV-infected individuals results in the appearance of double-positive CD4(+)/CD8(+) T cells, which become infected by endogenous HIV. HIV DNA sequences could be detected in uncultured and sorted mature CD3(+)CD8(+) T cells from HIV(+) individuals. These results suggest a new mechanism by which HIV could attack the immune system and may help to explain the CD8(+) T cell defects in AIDS patients.