Difference Between T Helper and T Cytotoxic Cells

Key Difference – T Helper vs T Cytotoxic Cells
 

Lymphocytes are a type of white blood cells with a single round nucleus. They are important defense cells in vertebrates immune system. T cells or T lymphocytes are a subtype of lymphocytes. They are part of the adaptive immunity and are mainly involved in cell mediated immunity which does not occur through antibody production. T cells are produced by bone marrows. Then they travel to the thymus and become mature. These T cells can be distinguished from other lymphocytes due to the presence of T cell receptors on the T cell surface. There are several types of T cells which have separate roles in the immune system. They include helper T cells, memory T cells, cytotoxic T cells (killer T cells) and suppressor T cells. Helper T cells cooperate with B cells in antibody production and activation of macrophages and inflammation. Killer T cells kill antigen infected cells (mostly virus infected cells), cancer cells and foreign cells directly. The key difference between T helper cells and cytotoxic cells is that helper T cells are involved in coordination of the immune response against the pathogen with B cells and other T cells while cytotoxic cells directly kill or destroy cancer cells and antigen infected cells.

CONTENTS

1. Overview and Key Difference
2. What are T Helper Cells
3. What are T Cytotoxic Cells
4. Similarities Between  T Helper and T Cytotoxic Cells
5. Side by Side Comparison – T Helper vs T Cytotoxic Cells in Tabular Form
6. Summary

What are T Helper Cells?

T helper cells (also called CD4⁺ T cells) are the main cells that coordinate immune response against an infection. T helper cells instruct other immune cells such as killer T cells, B cells, phagocytes (macrophages) and suppressor T cells by giving signals to work against the pathogen. Many helper T cells are needed for this function. Helper T cells perform all these functions by secreting small proteins called T cell cytokines (activating proteins). Helper T cells help to suppress or regulate the immune response as well. T helper cells also assist B cells and memory B cells for maturation.

When T helper cell detects a virus infection, it activates and divides into many T helper cells. This process is known as clonal expansion. Some of the divided cells remain as memory cells while other cells react in different ways as follows to respond to viral infection by producing activating proteins called cytokines.

1. Activate killer T cells to kill virus infected cells directly.
2. Stimulate B cells to produce antibodies to stick with free viral particles.
3. Stimulate macrophages to become effective in cleaning dead viral particles.
4. Stimulate suppressor T cells to slow down the immune response after the viral attack is neutralized.

What are T Cytotoxic Cells?

Cytotoxic T cells, also known as CD8⁺ T cells or killer T cells, are a type of T cells which directly kill cancer cells, virus infected cells and damaged cells via creating holes in the cell walls. When cell covers are broken, cell contents leak out and destroy the cells. Killer T cells express T cell receptors on cell surfaces to recognize antigens. Antigens bind to class I MHC molecules. Hence, cytotoxic T cells realize the threat.  Cytotoxic T cells release granules containing important molecules to kill the pathogen.

Two types of molecules are involved in cytotoxic T cells killing action. They are perforin and granzymes. Granzymes are proteases trigger apoptosis. Perforin molecules form holes or pores in the lipid bilayer.

What are the Similarities Between T Helper and T Cytotoxic Cells?

• T helper cells and cytotoxic T cells are white blood cells (leukocytes).
• T helper and T cytotoxic cells are two main types of T lymphocytes.
• Both are involved in adaptive immunity.

What is the Difference Between T Helper and T Cytotoxic Cells?

Summary – Helper T Cells vs Cytotoxic T Cells

Helper T cells and Cytotoxic T cells are the two main types of T cells. Helper T cells are involved in the coordination of the complete immune response against an infection. These cells instruct and stimulate B cells, other T cells and macrophages to perform their specific roles. Cytotoxic T cells directly kill the infected cells, cancer cells and other damaged cells. This is the difference between T helper cells and cytotoxic T cells. Both types are extremely important white blood cells of the immune system.

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References:

1.”The body’s second line of defence.” Science Learning Hub. N.p., n.d. Web. Available here. 13 July 2017.
2. Janeway, Charles A., and Jr. “T cell-mediated cytotoxicity.” Immunobiology: The Immune System in Health and Disease. 5th edition. U.S. National Library of Medicine, 01 Jan. 1970. Web. Available here. 13 July 2017.

Image Courtesy:

1. “Lymphocyte activation simple” By Häggström, Mikael (2014). “Medical gallery of Mikael Häggström 2014”. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.008. ISSN 2002-4436. (Public Domain) via Commons Wikimedia
2. “Killer T cells surround a cancer cell” By The National Institutes of Health – (Public Domain) via Commons Wikimedia