Difference Between NK Cells and NKT Cells

Key Difference – NK Cells vs NKT Cells

Let us first briefly look at the structure of the immune system before moving on to the discussion of the difference between NK Cells and NKT Cells. The immunity system is the body’s main system that can produce defensive action against invading pathogens and microbes. It is divided into two parts; innate immunity and adaptive immunity. Innate immunity produces diverse immune responses against the 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. The key difference between these two types of cells is, NK cells are not antigen-specific receptors whereas NKT cells are antigen-specific receptors.This article outlines the difference between NK cells and NKT cells.

What are NK Cells?

Natural killer (NK) cells are a type of lymphocytes associated with innate immunity. They are derived from bone marrow precursors and found in blood and spleen. Unlike other phagocytic cells, NK cells do not attack pathogens or invading microbes directly. Instead, they destroy the body cells that are infected with microbes. Hence, their action is not entirely by phagocytosis, but by apoptosis (programmed cell death) of the target body cells. 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. Once it is done, another NK-produced protein called granzymes enter the cell through the pores and activate caspases protein in the target cell that induce apoptosis.  Finally, the cell debris is ingested by macrophages. NK cells also have the ability to attack tumor cells, before tumor cells reach sufficient number, which enable them to be diagnosed. Thus, NK cells are one of most important defenses against cancer and often used in immune surveillance.Difference Between NK Cells and NKT Cells

 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 of both conventional T cells and NK cells. They are found mainly in the thymus, liver, spleen, and bone marrow. NKT cells are mainly responsible for producing an immune response against pathogens and auto-antigens. In addition, they are also involved in tumor 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.

Key Difference - NK Cells vs NKT Cells

The T lymphocyte activation pathway

What is the difference between NK Cells and NKT Cells?

Definition of NK cells and NKT cells

NK cell: Natural Killer Cells are a type of cytotoxic lymphocyte  that can react against and destroy another cell without prior sensitization to it.

NKT cells: Natural Killer T cells are a heterogeneous group of T cells that share properties of both T cells and natural killer cells.

Characteristics of NK cells and NKT cells

Antigen-specific receptors

NK cells: They do not express an antigen-specific receptor.

NKT cells: They express an antigen-specific receptor.

Functions of NK cells and NKT cells

NK cells: NK cells destroy virally infected cells and tumor cells.

NKT cells: NKT cells produce an immune response against pathogens and auto-antigens and are involved in tumor rejection, control of autoimmune diseases and immune surveillance.

Image Courtesy: 
“Antibody-dependent cell-mediated cytotoxicity” by Simon Caulton – Own work. (CC BY-SA 3.0) via Commons 
“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: Hazmat2 (talk) – This file was derived from  T cell activation.png:.(Public Domain) via Commons