What is the Difference Between Cytotoxic T Cells and Natural Killer Cells

The main difference between cytotoxic T cells and natural killer cells is that cytotoxic T cells are antigen-specific whereas natural killer cells are not antigen-specific.

Cytotoxic T cells and natural killer cells are two types of prominent cells in the immune system. Generally, they help to recognize and present antigens, respectively. Cytotoxic T cells also recognize presenting antigens on HLA class 1 molecules to kill the antigen-presenting cell. On the other hand, natural killer cells are a type of cytotoxic lymphocyte that kills virus-infected cells.

Key Areas Covered

1. What are Cytotoxic T Cells
   • Definition, Features, Function
2. What are Natural Killer Cells
   • Definition, Features, Function
3. Similarities Between Cytotoxic T Cells and Natural Killer Cells
   • Outline of Common Features
4. Difference Between Cytotoxic T Cells and Natural Killer Cells
   • Comparison with Key Differences

Key Terms

Adaptive Immunity, Cytotoxic T Cells, Natural Killer Cells

What are Cytotoxic T Cells

Cytotoxic T cells are a type of T lymphocyte that kills infected cells by intracellular pathogens and cancer cells. They also destroy damaged cells. Cytotoxic T cells possess T cell receptors (TCRs) to recognize specific antigens. Generally, HLA class 1 molecules present antigens to cytotoxic T cells. HLA class 1 molecules are expressed on the cell membrane of all nucleated cells, presenting endogenous antigens to the cytotoxic T cells. In addition, these endogenous antigens include bacteria, viruses, intracellular signals, etc. Cancer cells also present antigens to cytotoxic T cells.

Figure 1: Cytotoxic T Cells

Cytotoxic T cells then recognize antigens and induce the destruction of those cells, either through apoptosis or degranulation. Here, cytotoxic T cells send proteases and enzymes to the infected cells through a microtubule cytoskeleton. In addition, another type of T cells, called regulatory T cells, secrete IL-10, adenosine, and several other anti-inflammatory cytokines to activate cytotoxic T cells, reducing the severity of autoimmune diseases

What are Natural Killer Cells

Natural killer cells are large granular lymphocytes important in the innate immune system. They destroy infected cells and tumor cells without prior sensitization. Usually, T cells and B cells are the other two types of cells related to the NK cells. But, these two cell types trigger immune responses when they are sensitized. NK cells trigger innate immune responses which are nonspecific to the pathogen. Ideally, NK cells protect the body against pathogens such as bacteria, viruses, and tumor cells. Therefore, NK cells are considered the first group of cells that destroy tumor cells.

Figure 2: Natural Killer Cells

NK cells also secrete cytokines such as TNFa and INFg to initiate adaptive immune responses. Self-antigens of the body are recognized by the inhibitory receptors of the NK cells, preventing autoimmune responses.

Similarities Between Vaccine and Booster

• Cytotoxic T cells and natural killer cells are two types of cytotoxic cells.
• Both types of cells kill infected cells by intracellular pathogens.
• In addition, both kill cancer cells.

Difference Between Vaccine and Booster

Definition

Cytotoxic T cells refer to a type of immune cell that can kill certain cells, including foreign cells, cancer cells, and cells infected with a virus, while natural killer cells refer to lymphocytes able to bind to certain tumor cells and virus-infected cells without the stimulation of antigens, and kill them by the insertion of granules containing perforin.

Antigen Specificity

Usually, cytotoxic T cells are antigen-specific while natural killer cells are not antigen-specific.

Type of Immunity

Moreover, cytotoxic T cells belong to adaptive immunity while natural killer cells belong to innate immunity.

Conclusion

In brief, cytotoxic T cells are a type of T lymphocyte that recognize antigens present with HLA class 1 molecules. Therefore, they destroy cells with endogenous antigens such as cancer cells, bacteria, and virus-infected cells. On the other hand, natural killer cells are a type of large lymphocytes that destroy infected cells and cancer cells recognized by antibody binding. Therefore, the main difference between cytotoxic T cells and natural killer cells is their antigen specificity.

References:

1. Chaplin DD. Overview of the immune response. J Allergy Clin Immunol. 2010 Feb;125(2 Suppl 2):S3-23. doi: 10.1016/j.jaci.2009.12.980. PMID: 20176265; PMCID: PMC2923430.

Image Courtesy:

1. “CD8+ T cell destruction of infected cells” By nagualdesign – Own Work (CC BY-SA 4.0) via Commons Wikimedia
2. “Antibody-dependent Cellular Cytotoxicity” By Satchmo2000 – Own Work (CC BY-SA 3.0) via Commons Wikimedia