A CD4 count is used to check the immune system’s health in people infected with HIV (human immunodeficiency virus). HIV attacks and destroys CD4 cells. The immune system has trouble fighting infections if too many CD4 cells are killed. 

What are CD 4 Cells?

 

CD 4 cells or T-cells are a type of white blood cells that play a major role in protecting 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, which can be 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. The way a retrovirus attacks the body is by hi-jacking a cell, and mixing its genetic material (DNA)  with that of 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 CD 4 cells of the person’s immune system. HIV uses the machinery of the CD 4 cells to multiply (make copies of itself) and spread throughout the body. This is the HIV life cycle.

Secondly, the virus can remain latent. The HIV virus does not always replicate fast – it can lay dormant for some time and thereby go undetected by the body’s immune system to differentiate between infected and uninfected cells. ARV’s prevents active viruses from duplicating, but if treatment is stopped, hidden viruses can start replicating once more.

Thirdly, the HIV virus has a high rate of evolution. It enables the virus to evade the immune system faster than any other known pathogen.

Fourthly, the HIV virus has ways to escape 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 sample of your blood.

What does the CD 4 count tell you about your immune system?

 

The CD4 count is an important indicator of how well your immune system is working.

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).

 

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?