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Image of AIDS ELISA Test: Scanned in from
materials provided with kit (Figure 4), but originally
from http://en.wikipedia.org/wiki/file:ELISA-
sandwich.svg
Image of how HIV integrates
DNA into host cell DNA:
Scanned in from materials
provided with kit (Figure 3),
but originally from
http://upload.wikimedia.org/
wikipedia/commons/3/35/HI
V_gross_cycle_only.png and
http://aids.gov/hiv-aids-
basics/hiv-aids-101/what-is-
hiv-aids/index.html
Image of caption for
below: Scanned in from
materials provided with
kit (Figure 4)
What causes AIDS?
AIDS is caused by a virus called the Human Immunodeficiency Virus (HIV). This virus was transmitted to
humans from chimpanzees in an area of equatorial Africa encompassing the countries of Gabon, Cameroon, and
Equatorial Guinea. The transmission most like occurred when humans hunted the
chimpanzees and ate infected animals. Some recent studies indicate that this
transmission may have occurred as far back as the late 1800’s.
HIV is a member of a family of viruses called lentiviruses, which is a subgroup
of the retroviruses. The word lentivirus means slow virus because the virus, having a
long incubation period, takes a long time to cause disease. After infecting their hosts,
lentiviruses enter a period of their life cycle called a ‘latency period’ during which
no visible symptoms are apparent. In HIV infection, this latency period often
lasts for 10 years. The lentivirus, like other retroviruses, integrates its DNA into
the host cell’s genome, becoming part of the host DNA.
In order for the virus to survive, it must get past the body’s immune
system. HIV is able to enter immune cells because of a glycoprotein on its
surface, which mimics an antigen in the host which identifies “self.” It is able to
hide and multiply inside the very cells that are supposed to be patrolling for
disease-causing invaders. One of the virus’s main targets is the subgroup of
white blood cells called CD4
+
T cells. When the virus multiples inside of a cell, it
eventually ruptures the cell, releasing many virus particles, which can then infect
many more cells. Although the latent phase seems quiet, there is actually a
fierce battle raging between the immune cells and the virus. The virus is
multiplying rapidly, but the immune cells are quickly destroying them. However,
due to its ability to hide, in the form of a provirus in the memory CD4 and T4
lymphocytes, the virus slowly gains an advantage. A sharp drop in CD4
+
T cells
marks the final phase of the illness. This trait is used to follow the progress of
the disease.
How Do You Test for AIDS?
To test for HIV, a small amount of blood is drawn for an Enzyme-Linked Immunosorbant Assay (ELISA). If
the test returns a positive result, it is repeated. If there are positive results again, it is confirmed by using another
type of test. The results of both tests are 99.5% accurate.
These tests depend upon the infected person’s B cells forming antibodies to HIV. For the ELISA, a
rectangular plate called a microplate will be used. This contains rows of small wells that can hold a small volume
of chemicals. HIV coat protein is bound in the bottom of each well of the plate. Dilute serum from a patient’s
blood sample will be applied to the well. If anti-HIV antibodies are present, they will bind to the HIV protein coat
on the bottom of the well. Only individuals that have been infected with HIV will have antibodies that recognize
the HIV antigens in the protein coat at the bottom of the well. The wells are rinsed to remove unbound
antibodies or other protein. In order to detect if anti-HIV
antibodies are bound, a second antibody that recognize
the human antibody is added. If the anti-HIV antibodies
are present, the anti-human antibody will bind to them.
This second antibody also has an enzyme attached and is
referred to as a “conjugate.” The enzyme that is part of
the conjugate will cause a color change when a chemical
called a “chromogen” is added. Even if there is only a
small amount of HIV-antibody, this color change reaction
can be detected.