On the surface membrane of all living cells are complex protein structures called "receptors". A receptor is often compared to a lock into which a specific key or "ligand" will fit. There are at least two receptors on T-lymphocytes to which the human immunodeficiency virus (HIV) sticks. The primary receptor, called "CD4", is shown on the right in the diagram. But a second receptor that loops through the cell membrane 7 times is critical for infection to occur.
HIV infection of a lymphocyte requires attachment of the virus to the cell membrane through both of these "ligand-receptor" links. In cells whose "7-transmembrane receptor" is different, the HIV "key" no longer matches the lymphocyte "lock" and attachment is incomplete. Those cells may avoid infection by HIV.
Tight attachment of the viral particle to receptors on the lymphocyte membrane enables fusion with the cell membrane. The viral contents, including viral RNA (shown in yellow) then empty into the cell's cytoplasm.
Like other viruses that infect human cells, HIV commandeers the host's machinery to make multiple copies of itself.
2. REVERSE TRANSCRIPTION
From viral RNA to DNA
3. INTEGRATION, TRANSCRIPTION
a. Viral DNA joins host DNA
b. Making multiple viral RNAs