AssessmentsCell-mediated immunity of CD4 cells
Cell-mediated immunity of CD4 cells
Content Reviewers:Rishi Desai, MD, MPH
And there are two types of T cells.
Helper T cells primarily support other immune cells, whereas cytotoxic T cells kill cells that are infected with a pathogen or are cancerous.
That makes sense since CD4 helper T cells interact with other immune cells to stimulate them.
Now, when a T cell is initially formed it’s considered naive.
This naive T cell is a bit like a student in school that isn’t ready to choose a career path.
This process of priming requires two signals.
This antigen has to bind perfectly to the T cell receptor.
This region, which includes the T cell receptor which binds to the MHC-Antigen, and CD4 and CD28 which bind with B7, is called the immune synapse.
Going back to the student analogy, an activated student is one that’s gotten the signals it needs to graduate from college and is finally prepared to choose a career path.
The IL-2 receptor has three protein components - alpha, beta, and gamma.
A naive T cell only expresses the beta and gamma components of the IL-2 receptor, but these have low affinity for IL-2, in contrast to the alpha component of the IL-2 receptor which has a high affinity for IL-2.
Using just the beta and gamma components is like trying to eat an apple with only your lips and tongue.
And upregulating the alpha component is like using your teeth to take a big bite out of the juicy apple - much more effective and satisfying!
As a result active T cells bind to IL-2 that they make - a form of autocrine stimulation - a cell stimulating itself.
In response to the IL-2, the activated T cell starts to rapidly undergo cell division - a process called clonal expansion.
Now let’s go through the types of T helper cells - the career paths - one at a time.
CD4 cells are white blood cells that play a vital role in the body's cell-mediated immunity. Cell-mediated immunity is the part of the immune system which relies on phagocytes, cytotoxic T-lymphocytes, and the release of various cytokines to fight off an infection. CD4 cells recognize and destroy infected cells by binding to special proteins on the surface of the infected cells called antigens. Once attached, the CD4 cells release molecules called cytokines which activate other immune cells to destroy the infected cell.