The HIV gains entry into the macrophages and the helper T-cells after having infected the human body. [0.5]
HIV enters into helper T-lymphocytes (TH) in which they reverse transcribe DNA and then replicate to produce progeny . The progeny that are released in the blood attack other helper T-lymphocytes. This is repeated leading to a progressive production of more viral particles. [0.5 + 0.5 + 0.5]