The HIV lifecycle
HIV is a tricky virus. Instead of being destroyed by the immune system it uses immune cells to reproduce.
For the first 10 days, HIV stays hidden and is impossible to detect. But millions of copies of the virus are already being made in lymph nodes closest to the site of infection.
When these swollen lymph nodes burst, HIV is carried throughout the body. In response, your immune system makes even more immune cells, especially CD4 cells. This period is called seroconversion.
Instead of clearing the virus, CD4 cells are used by HIV to replicate. This process keeps repeating until you start ART.
The replication cycle
Each replication cycle lasts for about two days and has several stages. Each stage can be a target for HIV drugs.
- Firstly, HIV attaches to the surface of the cell. Then it is absorbed through the cell wall, losing its outer coating or shell.
- The inner capsule – called the capsid – then releases proteins and enzymes that HIV uses to replicate (called RT, integrase and protease) into the cell.
- The next stage is to convert the single strand of HIV molecules to match double-strand human DNA.
- This double strand of HIV then crosses into the central nucleus of the CD4 cell, where it joins (or integrates) into human DNA.
- The nucleus now produces the raw material to make new HIV. But these particles need to be cut up and reassembled by protease before new virus can fully function. This process starts inside the CD4 cell and continues after new virus leaves the cell.
- Each CD4 cell produces hundreds of new copies of HIV particles – called virions. These virions bud from the cell while HIV continues to develop. The CD4 cell then dies.
New HIV then infects other CD4 cells and this process is repeated millions of times each day.
Although HIV only infects one in a thousand CD4 cells, these cells signal to uninfected CD4 cells to also die early.
Without ART, the immune system becomes worn down. The immune system puts up a good fight – often for many years – but steadily and eventually loses.
But with ART, the HIV lifecyle is stopped and the immune system can repair itself.
Last updated: 27 May 2019.