The key difference between NK cells and NKT cells is that NK cells are not antigen-specific receptors, while NKT cells are antigen-specific receptors.
The immunity system is the body’s main system that can produce defensive action against invading pathogens and microbes. There are two types of immunity: innate immunity and adaptive immunity. Innate immunity produces diverse immune responses against pathogens through various types of cells in the body. One of the most important groups of cells involved in innate immunity is T lymphocytes. NK cells and NKT cells are two subsets of T lymphocytes. This article outlines the difference between NK cells and NKT cells.
CONTENTS
1. Overview and Key Difference
2. What are NK Cells
3. What are NKT Cells
4. Similarities Between NK Cells and NKT Cells
5. Side by Side Comparison – NK Cells vs NKT Cells in Tabular Form
6. Summary
What are NK Cells?
Natural killer (NK) cells are a type of lymphocytes associated with innate immunity. Their production occurs in the bone marrows. They are mainly present in blood and spleen. Unlike other phagocytic cells, NK cells do not attack pathogens or invading microbes directly. Instead, they destroy infected body cells. Hence, their action is not entirely by phagocytosis, but by apoptosis (programmed cell death) of the target body cells.
Figure 01: NK Cell
When NK cells are in contact with a target cell, they release a protein called perforins, which create pores on the membrane of the target cell. Through the created pores, another NK-produced protein called granzyme enters the cell and activate caspases protein in the target cell, inducing apoptosis. Finally, macrophages ingest the cell debris.
NK cells also have the ability to attack tumour cells before tumour cells reach a sufficient number, enabling a diagnosis. Thus, NK cells are one of the most important defences against cancer and often used in immune surveillance.
What are NKT Cells?
Natural killer T (NKT) cells are a subgroup of lymphocytes associated with the innate immune actions of the body. NKT cells share certain features with both conventional T cells and NK cells. They are present mainly in the thymus, liver, spleen, and bone marrow.
Figure 02: T Lymphocyte Activation Pathway
NKT cells are mainly responsible for producing an immune response against pathogens and auto-antigens. Also, they also participate in tumour rejection, control of autoimmune diseases, and immune surveillance. Based on the nature of the immune signal, NKT cells may produce either pro- or anti-inflammatory cytokines.
What are the Similarities Between NK Cells and NKT Cells?
- NK and NKT cells are cytotoxic cells in the immune system.
- They are also lymphocytes.
- Thus, they are lymphoid lineage cells.
- Moreover, they are components in the innate immunity.
- They induce cell death of pathogenic cells as well as tumour cells.
- They are found in the peripheral blood, spleen, liver, thymus, bone marrow, and lymph nodes.
- Defects in NK and NKT cells often lead to autoimmune disease or increased susceptibility to infectious diseases.
- Both cell types are essential in the initiation of adaptive immune responses and in regulating autoimmune responses.
What is the Difference Between NK Cells and NKT Cells?
NK cells and NKT cells are two types of cytotoxic cells involved in innate immunity. NK cells are a type of lymphocytes, while NKT cells are a subset of T lymphocytes. The key difference between NK cells and NKT cells is that NK cells do not express antigen-specific receptors, while NKT cells express antigen-specific receptors. Furthermore, NK cells mature in the blood while NKT cells mature in the thymus.
The following infographic summarizes the difference between NK cells and NKT cells.
Summary – NK Cells vs NKT Cells
NK cells are a type of cytotoxic lymphocytes that react against and destroy another cell without prior sensitization to it. In contrast, NKT cells are a heterogeneous group of T cells that share properties of both T cells and natural killer cells. NK cells do not express T-cell antigen receptors (TCR) while NKT cells express T-cell antigen receptors. So, this summarizes the difference between NK cells and NKT cells.
Reference:
1. “Natural Killer T Cell.” Natural Killer T Cell – an Overview | ScienceDirect Topics, Available here.
2. “Natural Killer Cell.” Wikipedia, Wikimedia Foundation, 15 July 2019, Available here.
Image Courtesy:
1. “Human Natural Killer Cell” By NIAID (CC BY 2.0) via Flickr
2. “T cell activation” By T_cell_activation.png: Template drawing and caption text from “The Immune System”, any modifcations, made by myself are released into the public domain.derivative work: Rehua (talk) – This file was derived from: T cell activation.png (Public Domain) via Commons Wikimedia