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The body's response to HIV and AIDs
AIDs, acquired immune deficiency syndrome, is caused by infection with the human immunodeficiency virus, HIV.
A syndrome is a collection of symptoms related to the same cause the action of HIV gradually destroys part of the immune system. The symptoms of
aids are those of the opportunistic infections to which the patient becomes susceptible as their immune system is weakened.
HIV is structurally complex it is an enveloped virus. The lipid envelope is formed from the host cell membrane as the new virus particles emerge from
the cell cytoplasm. Sticking through the envelope are viral glycoprotein molecules.
HIV INVADES T HELPER CELLS
1. Particular glycoprotein molecules (gp120) which are located on the virus surface, bind to the CD4 receptors on the surface of the T helper cells
2. They then combine with a second receptor
3. This allows the envelope surrounding the virus to fuse with the T helper cell membrane, enabling the viral RNA to enter the cell. Macrophages also
have CD4 receptors, so the virus can affect them.
HIV hijacks the cell's protein synthesis the virus needs to make the host cell replicate new viral components.
HIV nuclear material is RNA not DNA. Therefore the first step is to reverse normal transcriptase and manufacture DNA from the RNA template. To do this
the enzyme - reverse transcriptase is used. Viruses that use this enzyme are known as retroviruses.
Once the HIV DNA strand is produced, it is integrated into the host's DNA by another HIV enzyme, integrase. Once the HIV genome is integrated, it can
be transcribed and translated to produce new viral proteins. The new viral proteins assemble into new viruses. These bud out of the T cell, taking some
of the host cell surface membrane with them as their envelope, and killing the cells as they leave.
Infected T helper cells will also be destroyed by T killer cells. Therefore as the number of viruses increases, the number of host T helper cells decreases-
this means that the infected person's immune system becomes deficient.
The course of the disease AIDS
The acute phase
HIV antibodies appear in the blood after 3-12 weeks
Symptoms include fever, sweats, headache, swollen lymph nodes and sore throats there could be no symptoms.
Rapid replication of the virus and loss of T helper cells.
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The chronic phase The virus continues to replicate, but the numbers are kept in check by the
immune system (by T killer cells)
May be no symptoms but you suffer colds or other infections, which are slow to go away.
Dormant diseases e.g. TB and shingles can reactivate.
The disease phase Eventually, the increased number of viruses in circulation and a declining number
of T helper cells indicates the onset of AIDs.…read more