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The following points highlight four important ways by which HIV devastates the immune system. The ways are: 1. Direct killing 2. Apoptosis 3. Destruction of un-infected cells 4. Destruction of immune precursor cells.
Way # 1. Direct killing:
When a large number of viruses is produced and buds out from the surface of CD4+ T cell surface, the cell membrane is disrupted and this causes the cell to die. Also, the virus excessively uses the cell’s machinery for its own purposes, disrupting normal activities needed for the survival of the cell.
Way # 2. Apoptosis:
The dis-regulated infected cell may commit suicide by a process known as programmed cell death or apoptosis.
Way # 3. Destruction of un-infected cells:
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Cells that are not infected with HIV may also die as a direct result of the effects of HIV infection:
i. HIV may bind to the cell surface, making it appear as if the cell is infected. After antibodies attach to the virus on the cell, killer T cells, which serve to protect the immune system by killing infected cells, may mistakenly destroy the cell. This process is called antibody- dependent cellular cytotoxicity.
ii. CD8 T cells, also known as “killer T cells,” may mistakenly destroy uninfected cells that have consumed HIV particles and display HIV fragments on their surfaces.
iii. Because some HIV envelope proteins bear some resemblance to certain molecules on CD4+ T cells, the body’s immune responses may mistakenly damage these cells.
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iv. Uninfected cells may undergo apoptosis. HIV envelope alone or when bound to antibodies sometimes sends an inappropriate signal to CD4+ T cells. This can cause the cells to undergo apoptosis, even if not infected by HIV.
Way # 4. Destruction of immune precursor cells:
HIV may also destroy young cells that have not yet fully developed and will that later mature into cells with special immune functions. HIV can also damage the bone marrow and the thymus, which are needed for developing precursor cells.
