HIV Devastates the Immune System
Scanning electron micrograph of HIV-1, colored green, budding from a cultured lymphocyte.
Every day, HIV destroys billions of CD4+ T cells in a person infected with HIV,
eventually overwhelming the immune system's capacity to regenerate or fight other
infections. Below are different ways this may occur.
Killing Cells Directly
CD4+ T cells infected with HIV may be killed when a large amount of virus is produced
and buds out from the cell surface. The budding process disrupts the cell membrane
and causes the cell to die. The cell can also expire when the virus excessively
uses the cell’s machinery for its own purposes, disrupting normal activities needed
for the survival of the cell.
Apoptosis (cell suicide)
An HIV-infected cell undergoing apoptosis.
Credit: Institute of Cell and Molecular Science
When the regulation of a cell’s machinery and functions become grossly distorted because
of HIV replication, the infected cell may commit suicide by a process known as programmed
cell death or apoptosis. There is evidence that apoptosis occurs most frequently
in the bloodstream and lymph nodes of people infected with HIV.
The Death of Innocent Bystander Cells
Cells that are not infected with HIV may also die as a direct result of the effects
of HIV infection.
- 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.
- 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.
- 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.
- Uninfected cells may undergo apoptosis. Scientists have demonstrated in laboratory
experiments that the 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.
Destruction of Immune Precursor Cells
Studies suggest that HIV also destroys precursor cells (young cells that have not
yet fully developed) 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. The bone marrow and thymus probably lose their ability to regenerate,
further compounding the suppression of the immune system.
Information published courtesy of NIAID
This article was last modified in: 06/18/2012