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Transmission, signs and symptoms
Life cycle

The life cycle of HIV in CD4 T cells

  1. The virus approaches a CD4 T cell
  2. The virus particle attaches, via its glycoproteins, to a specific receptor protein (CD4) on the T cell.
  3. Fusion of the viral envelope with the plasma membrane of the T cell allows the viral genome and proteins to enter the cytoplasm.
  4. A complimentary double-stranded DNA (cDNA) copy of the single-stranded viral RNA is made using reverse transcriptase.
  5. Viral cDNA enters the nucleus and and is integrated into host DNA by viral integrase. The intergrated cDNA copy is known as the provirus. Whenever the cell divides, it also makes a copy of the viral DNA, increasing the number of infected cells. Until the T cell is activated the provirus remains dormant.
  6. T cell activation leads to transcription of the provirus, by cellular RNA polymerase.
  7. Viral proteins are are made using the host's protein synthesising machinery (Translation) and viral protease, which cleaves the viral polyproteins.
  8. New virus particles are assembled and bud off from the host cell.
  9. The T cell eventually dies.

HIV Life cycle

In patients infected with HIV, there is continuous production of virus particles and infection of new cells, this is even the case in HIV-infected individuals with no symptoms. If the new virus production is halted, for example using drugs that block virus replication or interfere with the production of viral proteins, the infected cells die quickly. HIV seems to be a dynamic disease, infected cells die rapidly, but are replaced just as quickly with more T cells that in turn become infected and so keep up virus production.

To see a flash animation of the process try: http://www.whfreeman.com/kuby/content/anm/kb03an01.htm