CD4 Cells

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What are CD4 cells? | CD4 Cell Definition

Clusters of differentiation 4 (CD4) are glycoproteins present on the immune cells’ surface such as monocytes, T helper cells, monocytes, macrophages and dendritic cells. CD4 T cells are pivotal, playing a central role in immune protection.

White blood cells are an indispensable part of the body’s immune system. A type of white blood cells, CD4 cells to be specific are infected and destroyed by the HIV (Human Immunodeficiency Virus). With the loss of these CD4 cells in such cases, the immune system and its responses decline, turning incapable to fight and attack pathogens. When a large amount of CD4 cells are lost, HIV infected people are at a risk of developing AIDS related OIs (opportunistic infections).

CD4 cells are indicators to your immune system. The range of normal CD4 cells count is 500-1500 cells/cubic millimetre of blood sample. With the worsening of HIV condition in a person, the CD4 cell count alarmingly decreases.

CD4 Count

CD4 count basically is a test measuring the count of CD4 cells in a blood sample. The normal count of CD4 cells is between 500 to 1500 per cubic milimetre of blood. Also referred to as T cells, CD4 cells fight infections, serving as critical defensive structures of the immune system. HIV strikes and destroys these CD4 cells. CD4 count helps determine the health of an HIV infected person’s immune system.

Significance of CD4 T-cells in HIV

CD4 T-cells are deemed to be helper cells as they stimulate the immune system to respond to infections rather than neutralizing infections. Responding to this, the CD8 T-cells act on them as they are considered as killer cells. They do so through the production of antibodies helping to fight against foreign particles/pathogens. For HIV to be able to infect host cells, it has to multiply, for this CD4 cells are its prime targets.
HIV attaches to these cells during infections unloading its genetic content so as to alter the genetic coding of the host to finally generate HIV virions. In the process, the CD4 cells of the host are destroyed. Consequently, the capability to stimulate immune responses to defend in such people declines eventually reaching a point wherein the body is susceptible to opportunistic infections.

Function of CD4 Cells

CD4 cells are co-receptors of TCRs (T cell receptors), assisting in mediating with the antigen-presenting cells. The TCR complex and CD4 cells secure to the definite sections of the antigen-presenting MHS class II molecules. The extracellular D1 domain of these CD4 cells binds with the β2 area of MHC Class II. This association enables the tyrosine kinase Lck to phosphorylate tyrosine remains of ITAMs (immunoreceptor tyrosine activation motifs) which is bound to the cytoplasmic tail of CD4 on the cytoplasmic domains of CD3. This intensifies the generation of signals by the T cell receptors.

The down streaming signals sent through tyrosine phosphorylation causes the transcription factors to get activated hence promoting activation of T cells.

To conclude, the CD4 cells are surface glycoproteins participating in activation and recognition of T cell antigen. In mature T cells, their mutually exclusive expression characterizes two subsets of T cells which differ in their function and specificity of antigens.

This was a brief on CD4 cells, CD4 count, its role and significance in the HIV disease along with its function. To learn other related topics important for NEET preparation, visit us at NEET BYJU’S.

Watch this video for a better understanding of the immune system.

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Frequently Asked Questions


What are signs of low CD4 count?

The signs of low CD4 cell count include fatigue, fever, cough, night sweats and weight loss.


What is the difference between CD4 and CD8 cells?

CD4 cells are white blood cells that help in fighting against infection, whereas CD8 cells are cytotoxic cells that induce apoptosis of infectious or cancerous cells.

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