An example of a natural killer (NK) cell is a tissue-resident NK cell found in the human liver, which plays a role in controlling liver fibrosis.
Natural killer (NK) cells are a type of cytotoxic lymphocyte critical to the innate immune system. They provide rapid responses to virus-infected or tumor-transformed cells. Unlike T cells, NK cells do not require prior sensitization to recognize and kill target cells. Here's a breakdown of NK cells:
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Function: NK cells eliminate infected or cancerous cells by releasing cytotoxic granules containing proteins like perforin and granzymes, which induce apoptosis (programmed cell death) in the target cell. They also produce cytokines, such as interferon-gamma (IFN-γ), that activate other immune cells.
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Location: While circulating in the blood, NK cells are also found in various tissues. Tissue-resident NK cells have been identified in the bone marrow, spleen, lung, intestines, and lymph nodes, and notably, in the liver.
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Liver NK Cells: The liver is enriched with NK cells, and these NK cells exhibit a specific phenotype. Liver NK cells participate in the control of liver fibrosis, a condition characterized by excessive scar tissue buildup in the liver, which can lead to cirrhosis and liver failure. These liver-resident NK cells can directly kill fibrogenic cells and secrete cytokines that modulate the fibrotic response.
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Activation and Inhibition: NK cell activity is regulated by a balance between activating and inhibitory signals received through various receptors on their surface. These receptors recognize ligands on target cells. If the activating signals outweigh the inhibitory signals, the NK cell will be triggered to kill the target cell.
In summary, liver-resident NK cells represent a specific example demonstrating the tissue-specific function and importance of these innate immune cells in maintaining tissue homeostasis and combating disease.
