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What Are CD4 Cells?

Andrew Kirmayer
Andrew Kirmayer

The human body has a highly efficient defense system against a militia of potential external invaders. White blood cells are the primary defense cells, and CD4 cells are the first-line defense against bacteria and viruses. Also known as T cells, these automatically become active once any kind of infection is detected and launch an immune response to attack any invader or foreign object. The amount of CD4 cells can be measured by medical tests to see whether or how much it deviates from normal.

There are two varieties of white blood cells, or lymphocytes, which work together to stave off infections. The T-4 cells actually go after what is trying to infect the body, and are essential to staying well and getting the immune system to fight an infection or illness once it has taken hold. Another kind of cell, known as a T-8 cell, triggers the immune system to end its state of alert and can also eradicate cells already infected or those that are cancerous. Substances called proteins enable researchers to determine what kind of cell they are looking at.

Anatomical model of the human body
Anatomical model of the human body

Researchers can gauge the health of the immune system by determining the CD4 count. This is the actual number of CD4 cells in a given drop of blood. It can vary quite a bit from one day to another, so the CD4 percentage is also an important measurement to look at. A reading of 29% or more is considered healthy, and the lower the percentage, the more likely it is that a problem with the immune system exists and that something is weakening it.

When someone has Human Immunodeficiency Virus (HIV), the first thing to look at is the percentage of CD4 cells in the blood. Readings below 14% can be a sign of trouble, and if the person is HIV positive, this can mean that Acquired Immune Deficiency Syndrome, or AIDS, has set in. Antiretroviral therapy (ART) can raise the CD4 count. A CD4 count of 350 serves as a general guideline in health care to begin ART, and the cell levels must be monitored on a regular basis.

The term CD4 refers to a part of the white blood cell called a receptor site. It is this receptor that HIV is able to attach to. For optimal health in general, having a normal count of CD4 cells is important for fighting off all infections and for staying healthy.

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    • Anatomical model of the human body
      Anatomical model of the human body