Thus, these two extremely polarized statuses of activated CD4 + T cells, with the un-stimulated resting cells (susceptible to the infection but not permissive for the rapid viral replication) as control in the middle of the “spectrum of permissiveness”, constitute a highly insightful system in the search for host factors responsible for HIV-1 susceptibility and its reversal in CD4 + T cells. Here, CD4 is linked to infection.