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Natural Killer Cells: Definition, Origin, And Its Various Functions.

Natural Killer Cells Definition

Natural killer cells are lymphocytes that are related to B and T cells in that they are lymphocytes. They are innate immune system cytotoxic cells that circulate throughout the body looking for contaminated and malignant cells. Natural killer cells produce cytotoxic granules when they come across an aberrant cell, destroying it and limiting the spread of infection or sickness in the body.

What Are Natural Killer Cells?

Natural killer cells (NK cells) are lymphocytes of the innate immune system. These white blood cells, which are connected to B and T cells, play an important role in infection management. When an NK cell comes into contact with a cancer cell or an infected host cell, it secretes cytotoxic granules in response to signals from the infected cell. The granules include perforin and granzymes, which work together to cause apoptosis in infected cells.

Where Are Natural Killer Cells Found?

NK cells (natural killer cells) are immunological sentinels that scan the body for unhealthy or cancerous cells. As a result, NK cells are located in almost all human tissues and are supplied all over the body. The circulation, the uterus, the lungs, and the liver have the largest quantities.

Origin of Natural Killer Cells

Natural killer cells are made up of stem cells found in the bone marrow, lymph nodes, spleen, and tonsils, among other places. Mature NK cells make up 5–20% of total circulating white blood cells in the human body.

Function of Natural Killer Cells

Natural killer cells are so-called because they are cytotoxic in their natural state, which means they do not need antigen exposure to activate (unlike cytotoxic T cells). Their main job is to stop infection from spreading throughout the body by eliminating contaminated host cells and locating and killing cancer cells.

NK Cells vs. Viral Infection

NK cells are cytotoxic cells that help the body fight viral infections. NK cells produce cytotoxic granules containing perforins and granzymes when they come into contact with a virus-infected host cell. Perforins are proteins that create holes in particular cells’ membranes. Granzymes are enzymes that pass through perforin-created pores to reach the target cell. The granzymes cause apoptosis (programmed cell death) in the infected cell, and the virus, including the host cell, dies.

Inducing cell death in this way holds viral agents confined inside the cells of the host, preventing them from spreading to other parts of the body. If NK cells just used perforins to kill target cells, the virus could flee and infect other cells.

Antigen-specific cytotoxic T cells are produced by the adaptive immune system. NK cells contain and restrict viral infections. After being activated, the cytotoxic T cells will go to work eradicating the pathogen from the body.

NK Cells vs. Cancer Cells

In addition, NK cells are immune cells that hunt for and destroy cancerous cells in the body. They attack cancer cells by generating perforin and granzyme-containing cytotoxic granules, much as they do virus-infected cells. The perforin creates pores in the cell membrane of the cancer cell, enabling the granzymes to enter. Apoptosis is triggered by granzymes, which activate apoptotic enzymes known as caspases, resulting in the death of the cell.

Natural Killer Cells (NKCs) are regulated.

Natural killer cells regularly come into contact with other cells as they go through the body’s tissues. The NK cells will produce cytotoxic granules in response to infected or otherwise aberrant cells. They will not, however, kill healthy self-cells. NK cells employ molecules expressed on their surface to know which cells are healthy as well as which are infectious.

Infected and malignant cells have chemicals on their surfaces that activation receptors on the surface of NK cells identify. Once the activation receptor binds to a chemical on the outer edge of an infected cell, the NK cell is “turned on” and directed to make cytotoxic granules.

Major Histocompatibility Complex I (MHCI) is a protein found on the surface of most healthy cells. The MHCI is recognised by inhibitory receptors on the top layer of NK cells, which “turn off” the cell, stopping it from discharging its deadly granules. This approach defends healthy cells from natural killer cells. Because pathogens (such as bacteria) lack MHCI on their surfaces, NK cells cannot be inhibited. MHCI is often lost in virus-infected host cells and cancer cells, leaving them incapable to ‘switch off’ the NK cells and vulnerable to attack.

Natural Killer Cells vs. Cytotoxic T Cells

Natural killer cells and cytotoxic T cells are quite similar. Both are lymphocytes that produce granules consisting of perforins and granzymes in order to destroy particular cells. However, there are a few key functional differences between the two.

Natural Killer Cells                                        Cytotoxic T Cells

Immune system that is a built-in                                      Immune system that adapts.

Antigens should not be targeted specifically,                  Concentrate on a single antigen.

Antigen-presentation is not required for activation.         Antigen presentation is required  for activation. 

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