Explain the mechanism by which HIV multiplies and leads to AIDS.

Explanation

A. After getting into the body of a person, the HIV-enters the `T_(H)` cells, macrophages or dendritic cells. In’these cells the ssRNA of
HIV synthesizes a DNA strand .complementary,.to the viral-RNA, using the enzyme reverse transcriptase. The reverse transcriptase also catalyses the formation of the second DNA strand .complementary. to the first strand forming the double stranded viral DNA. This viral DNA gets incorporated into the DNA of the host cells DNA by a viral enzyme (integrase) and it is in the form of a .provirus.. Transcription of DNA results in the production of RNA, which can act as the .genome. for the new viruses or it can

be translated into viral proteins. The various components of the viral particles are assembled and the HIV are produced. The infected human cells continue to produce virus particles and in this way they act like HIV generating factories. New viruses bud off from the host cell. This leads to a progressive decrease in the number of `T_(H)` cells in the body of an infected person leading to the immuno-deficiency in him. Even though HIV attacks cells with CD4 marker, for reasons not known, only `T_(H)`cells are destroyed and not the .macrophages.. The gp 120 molecules on the surface of HIV attach to CD4 receptors of human cells, mostly the `T_(H)` cells (gp120 fits the CD4.marker). Attack on certain types of cells/ tissues only by viruses such as HIV is refered to as .tissue tropism