This is a pathology defined by the Centers for Disease Control and Prevention (CDC) as patients with numbers of circulating CD4 T lymphocytes < 300 cells/mm3 or < 20% of total T cells on a minimum of two separate measurements at least 6 weeks apart, with no laboratory evidence of infection with human HIV-1 or HIV-2 and with the absence of any defined immunodeficiency or therapy associated with depressed levels of CD4 T cells.. Here, CD4 is linked to immunodeficiency disease.