What is the Difference Between CD4 and CD4+

The main difference between CD4 and CD4+ is that CD4 is a glycoprotein that serves as a coreceptor for the TCR (T-cell receptor), whereas CD4+ is a type of white blood cell called T helper cell. 

CD4 and CD4+ are two components of the immune system. They coordinate the immune response by stimulating immune cells such as CD8+ T cells, B cells, and macrophages. 

Key Areas Covered

1. What is CD4
– Definition, Facts, Importance
2. What is CD4+
– Definition, Facts, Importance
3. Similarities Between CD4 and CD4+
– Outline of Common Features
4. Difference Between CD4 and CD4+
– Comparison of Key Differences

Key Terms  

CD4, CD4+

What is CD4

CD4 is a glycoprotein that occurs on the surface of the T helper cells. Glycoproteins are made up of proteins attached to oligosaccharides. They occur on the cell membrane of eukaryotic cells. Also, they occur in the blood. Furthermore, the protein part occurs as an integral membrane protein, and the oligosaccharide part protrudes from the cell membrane. Besides stabilizing the membrane by forming hydrogen bonds with adjacent water molecules and serving as antigens for cell recognition, glycoproteins serve as neurotransmitter receptors and hormones. However, the function of CD4 is to serve as a coreceptor for TCR.

Figure 1: CD4 Receptor

Furthermore, TCR is another receptor molecule that occurs on the surface of T cells. Its function is to recognize specific antigens bound to the MHC complex. The binding of the TCR into the antigen is degenerated. Therefore, many types of TCR can bind to the same antigen. Structure-wise, TCR is a heterodimer containing two different protein chains. Around 95% of the TCR contains alpha and beta chains, while 5% of the TCR contains gamma and delta chains. Disease conditions such as leukemia can change the ratio.

What is CD4+

CD4+ T cells are the helper T cells (TH cells) that express CD4 glycoprotein on the cell membrane. They are responsible for the activation or suppression of the function of the other cells in the immune system. This mediation occurs through various types of cytokines secreted by CD4 T cells. Antigen-presenting cells, including macrophages, neutrophils, and dendritic cells, take up extracellular pathogens, including bacteria and viruses, to destroy them while processing their antigens. These processed antigens are presented on the cell membrane of the antigen-presenting cells along with MHC class II molecules. The CD4 T cells recognize these antigens through their T cell receptors and secrete cytokines.

Figure 2: CD4+ T Hepler Cells 

These cytokines include interleukins and IFN- γ. However, the type of cytokines produced depends on the type of CD4 T cells. The main types of CD4 T cells are TH1, TH2, TH17, and TFH. The effector cells of the CD4 T cells are B cells, CD8 T cells, and macrophages. Cytokines are responsible for B cells’ maturation into plasma and memory B cells. In addition, CD8 T cells mediate cytotoxicity, while macrophages destroy pathogens via phagocytosis.  

Similarities Between CD4 and CD4+

• CD4 and CD4+ are two components of the immune system.
• They coordinate the immune response by stimulating immune cells such as CD8+ T cells, B cells, and macrophages.

Difference Between CD4 and CD4+

Definition

CD4 refers to a large glycoprotein associated with a T cell receptor, especially on the surface of helper T cells. Meanwhile, CD4+ refers to a type of lymphocyte that helps to coordinate the immune response by stimulating immune cells, such as B cells, macrophages, and CD8 T lymphocytes (CD8 cells), to fight infection.

Importance

CD4 is a glycoprotein, while CD4+ is a white blood cell called T helper cells. 

Function

CD4 serves as a coreceptor for TCR, while CD4+ is a type of T cell that stimulates other immune system cells.

Conclusion

In brief, CD4 and CD4+ are two components of the immune system. CD4 is a glycoprotein that occurs on the surface of helper T cells. It serves as a co-receptor for the TCR. In comparison, CD4+ is a type of white blood cell. It is called T helper cells. Also, the function of the T cells is to stimulate other immune system cells. Therefore, the main difference between CD4 and CD4+ is their function. 

References:

1. CD4 T Lymphocyte: NIH. CD4 T Lymphocyte | NIH. (n.d.). https://clinicalinfo.hiv.gov/en/glossary/cd4-t-lymphocyte

Image Courtesy:

1. “CD4 correceptor” By DianaMcj – Own Work (CC-BY SA 3.0) via Commons Wikimedia
2. “Immune response of Lymphocytes” By SPQR10 – Own work (CC-BY SA 4.0) via Commons Wikimedia