There are six steps through which the HIV multiplies and affects the cells.
1. Entry of HIV into cells: Some cells of the immune system contain a molecule called CD4 on their surface. CD4 molecules are also found on the T cells. When the HIV virus enters the body, it first identifies cells with CD4 and attaches itself to them. Once the HIV binds with the CD4, the membranes of the virus and the T cell fuse. As a result of this fusion, the virus's RNA, proteins and enzymes enter the T cell. It is important to remember that although the main target for HIV is the T cells, it also attaches itself to other types of white blood cells containing CD4 but does not destroy them. These cells can act as reservoirs of HIV if the natural defence mechanism of the body tries to destroy the HIV
2. Reverse transcriptase: Once the RNA, proteins and enzymes of the HIV enter the cytoplasm of the T cell, an enzyme called, "reverse transcriptase" present in HIV converts RNA into DNA, which is an abbreviated form of deoxyribonucleic acid. DNA is a form of nucleic acid that carries genes, the basic unit of genetic inheritance.
3. Integration: In this stage, the newly-formed DNA of the HIV enters the T cell's nucleus and is incorporated its genes. Thus, when the T cell multiplies, the virus DNA is also copied. A person infected with HIV may contain billions of cells containing the HIV DNA.
4. Transcription: The T cell that contains HIV/ DNA cannot produce new viruses unless the RNA is able to make its own copies. It is important that these RNA are "read" by the protein- making mechanism of the infected T cell. To enable production of RNA copies and therefore to allow multiplication of new viruses, a special type of RNA called "messenger RNA" is produced. The process of production of messenger RNA is called transcription. This process involves the enzymes of the infected T-cell. The genes of HIV and the protein-making mechanism of the T cells together control the process of transcription.
5. Translation: After the messenger RNA of the HIV is processed by the nucleus of the infected cell, it is sent in to the cytoplasm. In the cytoplasm, the virus collaborates with the T cell's protein-making mechanism to make long chains of proteins and enzymes of HIV. The messenger RNA acts as a template or guide for production of HIV proteins and enzymes. The process of making long chains of viral proteins and enzymes is called translation.
6. Assembly and budding: In this stage, the newly made HIV proteins, enzymes and RNA collect just inside the wall of the infected T cell. At the same time, the proteins that form the covering of the virus collect within the wall of the infected T cell. Next, an immature particle of the virus is formed and it separates from the infected T cell. This new viral particle has an envelope that includes proteins from the walls of both, the HIV and the infected T cell. It is important to remember that the immature virus cannot spread the infection to other people.
The long chains of proteins and enzymes formed inside the infected cell are cut into smaller pieces by a specific enzyme of the virus called protease. This step results in formation of viral particles that can spread infection to other T cells.