After infecting the human body the HIV gains entry into the macrophages. Events that occur in the cells:i. The virus enters into macrophages where RNA genome of virus replicates to form viral DNA with the help of enzyme reverse transcriptase.ii. The viral DNA gets incorporated into host cells DNAand directs the infected cell to produce virus particles. iii. The macrophage continue to produce virus and in this way acts like a HIV factory.iv. The HIV enters into helper T-lymphocytos (TH ), replicates and produce progeny viruses. The progeny viruses released in the blood attacks other helper T-helper lymphocytes. This is repeated heading to a progressive decrease in the number of helper v. TH lymphocytes in the body of infected person. During this period the person suffers from bouts of fever, diarrhoea and weight loss. vi. The decrease in the number of the T helper cells leads to infections as the immune system of the person becomes weak.