Introduction of HIVObviously, before HIV infection can occur it must enter the body. Exposure to infected bodily fluids through sexual contact or sharing of neeedles is the primary way HIV enters the body. Infection through child birth and breastfeeding are also ways people become exposed to HIV.
Viral AttachmentOnce in the body, HIV needs a host to help it reproduce. The host in the case of HIV is the T-cell or CD4 cell. HIV seeks out CD4 cells and must attach to them by way of a "lock and key" type system. Proteins on the surface of HIV attach to complimentary proteins on the CD4 cell much like the way a key fits into a lock.
Viral attachment is blocked by the class of drugs called entry inhibitors. Blocking this stage prevents HIV from using the T-cell. If allowed to attach, HIV uses the cell for the next steps in reproduction.
Viral Fusion & PenetrationOnce attached to the cell, HIV injects proteins of its own into the cellular fluids (cytoplasm) of the T-cell. This causes a fusion of the cell membrane to the outer envelope of the HIV.
In order to block this step the class of drugs called entry or fusion inhibitors block this fusion between cell and HIV.
The UncoatingIn order to use its genetic material (RNA) for reproduction, the protective coating surrounding the RNA must be dissolved. Without this step, conversion of RNA to DNA (the building blocks of new HIV copies) can't take place, and reproduction is halted.
Reverse TranscriptionOnce in the cell, the single stranded RNA of the HIV must be converted to the double stranded DNA. It accomplishes this with the help of the enzyme reverse transcriptase. Reverse transcriptase uses building blocks from the T-cell to help change the HIV RNA to DNA. The DNA contains the genetic information needed for HIV reproduction.
Drugs called reverse transcriptase inhibitors block HIV's reverse transcriptase from using these building blocks. Nucleoside and nucleotide analog reverse transcriptase inhibitors (NRTIs) and contain faulty imitations of the proteins found in a T-cell's cytoplasm. Instead of incorporating a protein into the growing chain of DNA, the imitation building blocks in NRTIs are inserted, which prevents the double strand of DNA from becoming fully formed.Non-nucleoside reverse transcriptase inhibitors block reverse transcription by attaching to the enzyme in a way that prevents it from functioning.
IntegrationTo use the cell to reproduce, it must integrate the newly formed DNA into the cell nucleus. While the process is not fully understood, it is thought to be aided by transport proteins supplied by HIV.
Viral LatencyOnce integration has occurred, HIV must wait for more protein building blocks to be formed by the cells or in other words, HIV is waiting for materials it needs to complete the reproductive process.
Final AssemblyNow that all the materials are available, they must be separated (cleavage) and assembled into new HIV. This process is possible because of the enzyme protease. This enzyme separates the parts allowing them to be reassembled into new HIV.
Drugs called such as Kaletra, Crixivan, and Viracept bind to the protease enzyme and prevent it from separating, or cleaving, the subunits.
BuddingThe final step of the viral life cycle is called budding. With its genetic material tucked away and a new outer coat made from the host CD4 cell's membrane, the newly formed HIV pinches off and enters into circulation, ready to start the whole process again.
This is obviously a very simple look at the HIV life cycle. But it gives you an idea of what an intricate process HIV replication is. Our understanding of the life cycle continues to grow and from that knowledge new drugs targetting new stages in the life cycle are being developed. Giving HIV+ people medication options makes understanding the HIV life cycle a must.