Download HIV and the Immune System

HIV weakens the immune system, so it is important to know some of the basics
about how the immune system works normally in order to understand how HIV
affects people.
The immune system is the body’s defence against bacteria, germs and viruses which may cause disease.
It is made up of:
Physical barriers; such as intact skin and mucous membranes
Chemical barriers; such as stomach acid, and antibacterial substances in body fluids
Organs and cells; such as tonsils lymph glands, and a variety of white blood cells.
The immune system’s first line of defence is intact skin. When a foreign body (i.e. HIV) enters the bloodstream
the immune system can respond in the following ways:
Recognise Something Foreign
A person’s cells contain a
chemical cell surface code unique
to them, which enables the body
to recognise anything that does
not contain this code as foreign.
Resist the Infection
The antibodies that have been
produced attached themselves
to the foreign bodies, which in
turn help the ‘Helper’ cells to
locate the foreign bodies. The
‘Helper’ cells need to be told
when to stop, so ‘Suppressor’
cells (also called T8 or CD8+ cells)
are sent to do this when the
foreign bodies have been
destroyed.
Response to the Foreign
Threat
Certain ‘Helper’ cells (also called
CD4 cells) area activated which
help start the rest of the immune
system response.
Recruit Reinforcements
The ‘Helper’ cells tell other parts
of the immune system (B-cells) to
produce antibodies, and they tell
other white blood cells called
‘Killer’ cells (also called cytotoxic
T lymphocytes or CTLs) that they
need to recognise and destroy
abnormal or infected cells.
Prepare for Future Attacks
So that the body can respond
quickly and efficiently to the same
foreign bodies in the future,
‘Memory’ cells take a ‘photo
image’ of the foreign bodies.
WA AIDS COUNCIL
HIV & THE IMMUNE SYSTEM
www.waaids.com
Western Australian
AIDS COUNCIL
HIV and the Immune System
Following the above, HIV has the ability to ‘lock on’ to the surface of the CD4 (’Helper’) cells, the very cell that
helps start off the immune response. HIV then moves inside the cell, where it begins to reproduce. During this
process it copies the unique DNA code of the host cell, so that new HIV cells are no longer identified by the
body as foreignm therefore the immune system no longer responds to them.
HIV multiplies inside the CD4 cell. When the CD4 cell is full of HIV, it breaks open, killing the CD4 cell, and
releasing more HIV into the bloodstream.
The virus will continue to invade and destroy CD4 cells. Eventually the body can’t replace the CD4 cells fast
enough, and the immune system deteriorates. When the immune system has deteriorated to the point that it
is unable to fight off diseases, a person is diagnosed with AIDS.
Some Definitions
The Window Period
The window period is the time lag between when the
immune system produces HIV antibodies, and when
these antibodies can be detected by an HIV antibidy
test. The HIV antibody test looks for the presence of
HIV antibodies, not the virus itself. It can take between
2-12 weeks before the immune system produces
enough antibodies to be detected. If aninitial test for
HIV comes back negative, it may be that the body has
not yet produced sufficient antibodies to be detected.
For this reason, if a test taken in the window period
comes back negative, a second test should be taken
12 weeks later. Transmission can occur during this
period so safer sex should be practised.
AIDS
A
I
D
S
- Acquired - Caused by an agent, not hereditary
- Immune - Pertains to the immune system
- Deficiency - Incomplete or lacking.
- Syndrome - A collection of illnesses, sometimes
occuring simultaneously.
Seroconversion
When antobodies have been produced and detected,
then seroconversion has taken place. “Sero” is the latin
word for blood, so the term means that the blood has
changed/is changing. Seroconversion illness is an
illness that can be experienced as a result of infection.
Usually this takes the form of mild influenza type
symptoms or a rash. It should be noted that not all
people will experience seroconversion illness so it
should be relied upon as an indicator of transmission.
Asymptomatic Phase
From the point of seroconversion, the person is HIV
positive. This can only be confirmed by an HIV
antibody test. The asymptomatic phase means ‘no
symptoms’. During this phase a person who is HIV
positive does not show any major symptoms related
to HIV infection. The average is 9-10 years but varies
considerably from individual to individual.
A person who is HIV positive is usally given a diagnosis of AIDS if they develop two or more opportunistic
illnesses simultaneously, and/or have a CD4 cell count below 200. An opportunistic illness is one which
takes advantage of the ‘opportunity’ presented by a damaged immune system and usually present no threat
when the immune system is working properly. The are over 40 illnesses which have been classified as
opportunistic illnesses.
WA AIDS COUNCIL
HIV & THE IMMUNE SYSTEM
www.waaids.com
Western Australian
AIDS COUNCIL