If left untreated, HIV infection results in a progressive loss of the CD4+ T helper cells, leading to severe immunosuppression that predisposes a patient to wide range of opportunistic infections, malignant neoplasm, and neurological complications that rarely occur in persons with intact immune function [31, 32].There are sufficient evidences suggesting susceptibility or resistance to infection with HIV-1 as well as the subsequent rate of disease progression to AIDS is multifactorial, including viral, host genetic, and immunological factors. The gene discussed is CD4; the disease is Opportunistic infection.