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Index 1.4 Organs of the body 1.5 The immune system 1.6 HIV and the immune system

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Glossary Hide

ARV anti-retroviral (drug to treat HIV infection).

antibody cells in your immune system that recognise antigens.

antigen infectious material produced by a virus or bacteria.

CD4 cell cell (lymphocyte) in your immune system that signals CD8 cells to destroy a virus. CD4 cells are also used by HIV as factories to reproduce in

CD8 cell cell (lymphocyte) in your immune system that kills cells that are infected with HIV.

immune system different parts of your body used to fight infections.

CD4 count number of CD4 cells in a drop of your blood. CD4 counts are measured in cells/mm³.

lymphocyte white blood cell.

macrophage large white blood cell that engulfs infectious organisms and waste material from dead cells.

HIV human immunodeficiency virus.

TB tuberculosis, a bacterial infection that commonly affects the lungs but which can affect other organs.

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CD4 and viral load PowerPoint 93 Kb

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1 Immune system and CD4 count

1.5 How the immune system works (before HIV infection)

Protection from infection

Your skin is a major barrier.

If your skin is damaged, for example through a tiny cut or tear, an infection can enter your body (like the HIV virus).

An infection can also be breathed in (like TB).

If an infection enters the body it is attacked by the immune system.

Antigens and antibodies

Two medical words are often used when talking about the immune system and infections:

Antigen is a word for a small particle of infectious material that has been broken down in the body and recognised by the immune system.
Antibody is a type of protein made by certain white blood cells in response to a foreign substance (antigen). Each antibody can bind to only one specific antigen. The purpose of this binding is to help destroy the antigen. Some antibodies destroy antigens directly. Others make it easier for white blood cells to destroy the antigen.

Cellular and humoral immunity

Your body uses different cells to attack and break down an infection. There are two main ways that your body does this:

Humoral immunity is based on antibodies

In response to an infection you body makes antibodies to identify and sometimes destroy the foreign particles.
HIV is routinely diagnosed using an antibody test. This looks for evidence of the body's response to HIV. This response usually takes 2-3 weeks from infection to develop, but can take several months and occasionally longer.

Cellular immune responses are based on CD4 and CD8 responses

Generally your body uses cellular immunity to fight viruses, and to fight HIV.

T cells are a type of white blood cell (lymphocyte). The two main types of T cells are CD4⁺ cells and CD8⁺ cells (T4 and T8 cells).
CD4 cells are sometimes called helper cells because they help the immune response by sending signals to CD8 cells.
CD8⁺ cells are sometimes called killer cells because they recognise and kill cells that are infected with a virus

Sometimes these cell processes and functions overlap.

Macrophages are another type of larger white blood cell that engulf or swallow up infectious organisms or waste material from dead cells. They also send signals to activate other cells in the immune system.

What does 'CD' stand for?

CD stands for cluster of differentiation. Cells in the immune system are classified by these molecules (glycoproteins), which are found on the surface of the cell.

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