Natural Killer Cells are a Form of Granular Lymphocytes of Varying Sizes
Natural Killer Cells |
Natural killer cells undergo
positive and negative selection to weed out self-targeting cells as they
develop in the primary lymphoid tissue of the bone marrow. When fully
developed, they relocate to secondary lymphoid tissues where they go through
terminal maturation.
Both stimulatory and inhibitory
receptors, such as killer cell immunoglobulin like receptors (KIR) and NKG2D,
are present on mature NK cells and regulate the activity of the cell. It is
known that there are over 20 activating receptors that are used to identify
proteins that are not typically found on a cell's surface. Self-MHC I proteins
are primarily recognised by inhibitory receptors. This is due to the fact that
numerous virus types have developed immunological evasion mechanisms by
downregulating MHC class I, which prevents the immune system from recognising
their viral antigens.
According to Coherent Market Insights the Natural
Killer Cells Market Global Industry Insights, Trends, Outlook, and
Opportunity Analysis, 2022-2028.
Overall, if there is a balance
between inhibitory and stimulatory signals, the inhibitory signals will take
precedence over the activation signals, preventing the activation of the NK
cell and preventing the killing of the self-cell. However, NK
cells will be activated if there is a low inhibitory signal as a result
of decreased MHC I on the cell surface or a high activation signal as a result
of increased production of stress ligands. When NK cells become active, they
introduce cytotoxic chemical-containing lytic granules into the infected cell.
Before perforins and granzyme B are released, an immunological synapse is
established between the NK cells and the infected cell. Granzyme B, an enzyme
that causes cell death, enters the cell through pores in the membrane that
perforins create. Granzyme B then triggers caspase-mediated apoptosis, which
kills the cell. In addition to producing the cytokines IFN and TNF, activated
NK cells also stimulate the acquired immune response by drawing in additional
immune system players.
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