[Role of CD4 T cells in the immune response]

CD4 T cells orchestrate the immune response, facilitating cytotoxic and humoral responses while preventing the destruction of one's own tissues by more autoreactive T cells. However, unlike complete CD4 T cell deficiency, the apparent deficiency caused by mutations in the CD4 gene that prevent its expression does not result in severe combined immunodeficiency in humans. The absence of the CD4 molecule limits the number of clones selected in the thymus on the basis of major histocompatibility complex type II, but does not prevent the acquisition of the T helper lymphocyte program, allowing them to retain most of their effector capacity. This observation raises new questions about the function of CD4 T cells and, in particular, the intrinsic role of the CD4 molecule.