How does HIV affect the immune system?
The HIV virus needs special immune cells, the CD4 cells, to multiply. The HIV particles in your blood look for those CD4 cells, which they can easily penetrate because they fit exactly. Once inside, the HIV virus uses the CD4 cell as a kind of copier to multiply itself. The HIV virus forces the healthy CD4 cell to make new virus particles. Eventually that CD4 cell opens up and is then so damaged that it dies. The released new virus particles enter the body and all seek a CD4 cell again. This way everything starts all over again and more and more immune cells break down.
Your body naturally tries to fight HIV infection. Your immune system has recognized the HIV cells and wants to attack and destroy them. But because the virus multiplies so quickly, mistakes are made and the copy always looks slightly different. That is called mutation. The immune cells no longer recognize the virus particle and do not destroy it immediately. This way the virus particle can continue to multiply undisturbed.
Every day billions of new virus particles are created and billions of CD4 cells die. Those CD4 cells, however, have a very important role in the immune system; they control all other immune cells so that every cell knows exactly what to do. When many CD4 cells die, the other immune cells do not know what to do anymore. Your immune system will not work properly anymore, so you can no longer defend against pathogens. You will then become more susceptible to ordinary, common viruses, bacteria or fungi. Eventually you can even get infections of viruses, bacteria or fungi that you would not even get sick of. We call that with a difficult word ‘opportunistic infections’. Opportunism means: acting according to the possibilities of that moment. An opportunistic infection is an infection that can occur at that time because someone has a reduced immune system.