A CD4 count checks the immune system’s health in people infected with HIV (human immunodeficiency virus). HIV attacks and destroys CD4 cells, and the immune system has trouble fighting infections if too many CD4 cells are killed.
What are CD 4 Cells?
CD4 cells or T-cells are white blood cells that protect your body from infection.
- A CD4 cell picks up foreign protein that enters the body.
- They then send signals to activate your body’s immune response upon detecting the intruder, a virus or bacteria.
- The immune system reacts by producing antibodies to kill the virus.
- A healthy immune system can produce 2000 antibodies per second.
Why is it so difficult for the immune system to fight HIV?
There are a few reasons why the body struggles to fight HIV.
Firstly, HIV is a retrovirus. A retrovirus attacks the body by hijacking a cell and mixing its genetic material (DNA) with the host cell. A virus cannot replicate on its own. Once a person is infected with HIV, the virus begins to attack and destroy the CD4 cells of the person’s immune system. HIV uses the machinery of the CD4 cells to multiply (make copies of itself) and spread throughout the body. This is the HIV life cycle.
Secondly, the virus can remain latent. HIV does not always replicate fast – it can lay dormant for some time and go undetected by the body’s immune system to differentiate between infected and uninfected cells. ARVs prevent active viruses from duplicating, but if treatment is stopped, hidden viruses can start replicating once more.
Thirdly, the virus has a high evolution rate, enabling it to evade the immune system faster than any other known pathogen.
Fourthly, the virus can avoid being neutralised by the immune system by coating its proteins with sugars. CD4 cells struggle to identify the foreign protein and trigger an immune response.
What is a CD 4 Count?
A CD 4 count is a lab test that measures the number of CD 4 T lymphocytes (CD 4 cells) in a blood sample.
What does the CD 4 count tell you about your immune system?
The CD4 count is an essential indicator of your immune system’s health.
The CD 4 count of a healthy adult/adolescent ranges from 500 – 1,200 cells/mm3.
A very low CD 4 count (less than 200 cells/mm3) is one of the ways to determine whether a person living with HIV has progressed to stage 3 infection (AIDS).
Quiz
You can do a self-test quiz – the STD Quiz, to learn more about your risk of contracting an STD.
Resources:
CD4 Lymphocyte Count: MedlinePlus Medical Test.
What is CD4 Count? Why is it important?
World AIDS Day: Why Is It so Difficult to Fight HIV?