CD4 and infection: The overtly symptomatic stage of HIV illness denotes the late stage of HIV disease (AIDS) in which patients (i) have a CD4+ T-cell count of less than 200 cells/mm3 and (ii) are vulnerable to additional opportunistic infections (OIs) (167) (such as infections by Mycobacterium avium complex, Mycobacterium tuberculosis, Pneumocystis jirovecii, Cytomegalovirus, Toxoplasma gondii, and Candida species) or the occurrence of aggressive forms of Kaposi’s sarcoma or B-cell lymphoma (32).