The cells that HIV attacks first when it gains entry into a human body are the macrophages where RNA genome of the virus replicates to form viral DNA with the help of the enzyme reverse transcriptase.
This viral DNA gets incorporated into host cell’s DNA and directs the infected cells to produce virus particles. The macrophages continue to produce virus. HIV enters into helper T-lymphocytes (TH ), replicates and produce progeny viruses. The progeny viruses released in the blood attack other helper T-lymphocytes. This is repeated leading to a progressive decrease in the number of helper T lymphocytes in the body of the infected person. Due to decrease in helper T cells, the person suffers from infections that could have been overcome by the body's immune system. So now the individual becomes immuno-deficient. So this is how the virus replicates further to cause immune deficiency in the body.
The diagram below shows how retrovirus replicates:
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