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Natural killer cells, also known as NK cells, are a type of cytotoxic lymphocyte critical to the innate immune system.They are a kind of large granular lymphocytes [1] [2] (LGL), and belong to the rapidly expanding family of known innate lymphoid cells (ILC) and represent 5–20% of all circulating lymphocytes in humans. [3]
The source of interferon-gamma can be CD4 + T cells, CD8 + T cells, natural killer cells, B cells, natural killer T cells, monocytes, other macrophages, or dendritic cells. [38] Nitric oxide is then released from the macrophage and, because of its toxicity, kills microbes near the macrophage. [14]
Granzymes are serine proteases released by cytoplasmic granules within cytotoxic T cells and natural killer (NK) cells. They induce programmed cell death (apoptosis) in the target cell, thus eliminating cells that have become cancerous or are infected with viruses or bacteria. [1] Granzymes also kill bacteria [2] and inhibit viral
The innate leukocytes include: natural killer cells, mast cells, eosinophils, basophils; and the phagocytic cells include macrophages, neutrophils, and dendritic cells, and function within the immune system by identifying and eliminating pathogens that might cause infection. [2]
Antigen presentation stimulates T cells to become either "cytotoxic" CD8+ cells or "helper" CD4+ cells.. A cytotoxic T cell (also known as T C, cytotoxic T lymphocyte, CTL, T-killer cell, cytolytic T cell, CD8 + T-cell or killer T cell) is a T lymphocyte (a type of white blood cell) that kills cancer cells, cells that are infected by intracellular pathogens such as viruses or bacteria, or ...
Cellular immunity protects the body through: T-cell mediated immunity or T-cell immunity: activating antigen-specific cytotoxic T cells that are able to induce apoptosis in body cells displaying epitopes of foreign antigen on their surface, such as virus-infected cells, cells with intracellular bacteria, and cancer cells displaying tumor antigens;
In antibody-dependent cell-mediated cytotoxicity, the pathogen does not need to be internalised to be destroyed. ADCC requires an effector cell with the ability to eliminate pathogens through release of cytotoxic agents, most notably natural killer cells. However, macrophages, neutrophils and eosinophils are sometimes implicated. [6]
T H 1 cells play an important role in classical macrophage activation as part of type 1 immune response against intracellular pathogens (such as intracellular bacteria) that can survive and replicate inside host cells, especially those pathogens that replicate even after being phagocytosed by macrophages. [45]