Outside the cell, HIV is known as a virion and is surrounded by a protective envelope, which also surrounds a certain amount of viral proteins and some genetic material, a "plan" containing all the information necessary for the creation of new viruses.
Viruses can be divided into two classes: those whose genetic material consists of DNA, and those whose genetic material consists of RNA, such as HIV. RNA viruses are called retroviruses and their reproduction process is slightly more complex than that of viruses composed of DNA.
Viruses often tend to infect certain cells in human, animal and plant hosts. HIV mainly infects cells containing the CD4 molecule on their surfaces. CD4 is found in immune cells, mainly in T-helper cells that are responsible for the functioning of the immune system, and also in macrophages, cells that travel through the body fighting bacteria and other germs.
To penetrate cells, HIV binds to the CD4 receptor through the gp120 molecule that is found on its surface. Once attached to CD4, HIV activates other proteins on the surface of the human cell, known as CCR5 and CXCR4, thus completing the fusion.
Anti-HIV drugs that attack the virus at this stage of their life cycle are called fusion inhibitors. The T-20 inhibitor (enfuvirtude, Fuzeon), combined with other antiretrovirals, has shown positive results in experiments, because to block HIV, T-20 joins the virus, while other fusion inhibitors may join to CCR5 or CXCR4 proteins.
Once fusion has occurred, the inner part of the virus, made up of RNA and some important enzymes, is absorbed by the human cell. Then, the viral enzyme called reverse transcriptase decodes the genetic material of HIV, that is, RNA to DNA.
Three classes of anti-HIV drugs attack the virus at this stage: the nucleoside analogs (AZT / zidovudine, ddI / didanosine, 3TC / lamivudine, d4T / lamivudine, ddC / zalcibatin and abacavir); non-nucleoside reverse transcriptase inhibitors (efavirenz, neviparin, delavirdine); and nucleotide analogs (tenofovir).
The newly formed viral DNA integrates with the human host cell's DNA through a viral enzyme called integrase, thus allowing HIV to "reprogram" the human cell to create more viruses. Still in the early stages of development, integrase inhibitors delay this stage of the HIV life cycle.
Then, the building blocks of the proteins that will form the new HIV particle are grouped within the human cell, organizing themselves by decoding the information contained in the messenger RNA.
The viral enzyme called protease cuts the building blocks of proteins into smaller pieces, forming the structure of the new HIV particle that includes all the enzymes and proteins necessary for the repetition of the reproductive process. In the sequence, the new viral particle develops in the human cell and enters the bloodstream, thus being able to infect other cells. It is estimated that approximately 10,3 billion new virions are formed daily in people who do not use HAART (highly potent antiretroviral therapy).