Difference Between IL-2 and IL-15

The key difference between IL-2 and IL-15 is that IL-2 is an interleukin in the immune system mainly produced by activated CD4 Th1 cells while IL-15 is an interleukin in the immune system mainly produced by activated dendritic cells and monocytes.

Interleukins (ILs) are a group of cytokines. They were first seen to be expressed in leukocytes, and the term interleukin was coined by Dr. Vern Paetkau, University of Victoria. The human genome encodes more than 50 interleukins and related proteins. The function of the human immune system largely depends on interleukins. Their deficiency causes rare disease conditions such as autoimmune diseases and immune deficiencies.  The majority of them are synthesized by CD4 T lymphocytes, monocytes, macrophages, and endothelial cells. Their main function is promoting the development of T and B lymphocytes and hematopoietic cells. Therefore, IL-2 and IL-15 are two types of interleukins in the immune system.

CONTENTS

1. Overview and Key Difference
2. What is IL-2 
3. What is IL-15
4. Similarities – IL-2 and IL-15
5. IL-2 vs IL-15 in Tabular Form
6. Summary – IL-2 vs IL-15

What is IL-2?

IL-2 is an interleukin in the immune system that is mainly produced by activated CD4 Th1cells. It is a 15.5 to 16 kDa protein. This protein was discovered in 1976. It regulates the activities of white blood cells (leukocytes). IL-2 is a lymphokine that induces the proliferation of responsive T cells. Additionally, it acts on some B cells via receptor-specific binding and acts as a stimulant for growth factors and antibody production. This protein is secreted as a single, glycosylated polypeptide. The cleavage of this signal sequence is very important for its activity. NMR studies suggest that the structure of IL-2 comprises a bundle of 4 helices flanked by two shorter helices and several poorly defined loops. The secondary structure analysis suggests the structure of IL-2 is similar to IL-4 and granulocyte-macrophage colony-stimulating factor (GMCSF). The gene-producing IL-2 is located in chromosome 4q26 region.

Furthermore, IL-2 is a part of a natural response to microbial infection in the body. It can also discriminate between foreign and self. IL-2 receptor is a complex comprised of three chains: alpha (CD25), beta (CD122), and gamma (CD132). This receptor is expressed by regulatory T cells, activated T cell, CD8⁺ T cells, NK cells, and B cells. Some research evidence tells that IL-2 is involved in itchy psoriasis. Moreover, aldesleukin is a recombinant IL-2 that is recommended by the FDA for the treatment of malignant melanoma and renal cell carcinoma.

What is IL-15?

IL-15 is an interleukin in the immune system that is mainly produced by activated dendritic cells and monocytes. It is a 14-15 kDa protein. This protein was discovered in 1994. Its receptor IL-15 Rα is predominately expressed by activated dendritic cells and monocytes. IL-15 is consecutively expressed by a large number of cells other than activated dendritic cells and monocytes such as monocytes, macrophages, keratinocytes, fibroblasts, myocytes, and nerve cells. IL-15 is a pleiotropic cytokine, and it plays a key role in innate and adaptive immunity. In addition, this cytokine induces the proliferation of natural killer cells of the innate immune system, whose principal function is to kill virally infected cells in the body.

Gene producing this glycoprotein is a 34kb region in chromosome 4(4q31) in humans. Furthermore, IL-15 has been shown to enhance the anti-tumor effects of CD8+ T cells in preclinical research. Therefore, IL-15 is engineered in laboratories as a tumor vaccine. It found that IL-15 receptor expression is absent in Epstein Barr virus infection. However, a recent report has indicated that IL-15 promotes non-alcoholic fatty liver disease and celiac disease.

What are the Similarities Between IL-2 and IL-15?

• IL-2 and IL-15 are interleukins.
• Both are protein molecules.
• They are cytokines (signalling molecules).
• They play a pivotal role in the immune system.
• Both belong to the four α-helix bundle family of cytokines.
• They have similar downstream effects in signalling pathway.
• These are used in the treatment of cancer.

What is the Difference Between IL-2 and IL-15?

IL-2 is an interleukin in the immune system that is mainly produced by activated CD4 Th1 cells while IL-15 is an interleukin in the immune system that is mainly produced by activated dendritic cells and monocytes. So, this is the key difference between IL-2 and IL-15. Furthermore, IL-2 is a lymphokine, while IL-15 is not a lymphokine.

The following infographic lists the differences between IL-2 and IL-15 in tabular form for side by side comparison.

Summary – IL-2 vs IL-15

Interleukins are naturally occurring proteins that mediate communication between cells. They are important parts of the immune system. IL-2 and IL-15 are two types of interleukins in the immune system. IL-2 is mainly produced by activated CD4 Th1cells, while IL-15 is mainly produced by activated dendritic cells and monocytes. Thus, this is the summary of the difference between IL-2 and IL-15.

Reference:

1. Waldmann, Thomas A. “The Shared and Contrasting Roles of IL2 and IL15 in the Life and Death of Normal and Neoplastic Lymphocytes: Implications for Cancer Therapy.” Cancer Immunology Research, U.S. National Library of Medicine.
2. Waldmann, Thomas A. “The IL-2/IL-15 Receptor Systems: Targets for Immunotherapy.” Journal of Clinical Immunology, Kluwer Academic Publishers-Plenum Publishers.

Image Courtesy:

1. “Gen IL-15” By Malymajo – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Interleukin-2” By Swiss Model User – (CC BY-SA 4.0) via Commons Wikimedia