Cell Biology 241
Natural Killer Cells
Despite their infuriated name, natural killer cells are literally a very important type of cell in the human body. Natural killer cells, also known as NK cells, are primarily a supportive type of cell which aids in protecting you from distinct infections and even cancer, as these cells target tumor cells.1 The natural killer cell plays a severe role in administering the innate and adaptive immune response to pathogens, injury, and stress. Natural killer cells acquired their name from the fact that they are propagated naturally by the body and their sole purpose is to search for and suppress destructive cells. When a destructive cell is detected, natural killer cells bind to the invader and produce a cytotoxic chemical.1 This chemical is called tumor is called tumor necrosis factor (TNF) and it is indeed a type of chemotherapy drug.1 Once the TNF has been emanated, holes begin to develop in the membrane of the invading cell. Because of the holes, fluids slip in, ultimately resulting in the cell bursting. Although originally portrayed as primarily a lytic cell, the NK cell has transpired as a cell adequate of the helper function, expansion, contraction, and accelerated memory responses; features similar to other adaptive immune cells.1 These characteristics place the NK cell in a exclusive position, with a superior role in sculpting the host response to damage and injury.
Natural killer cells comprise 5% to 20% of human peripheral blood lymphocytes and are acquired from CD34+ hematopoietic progenitor cells.2 The precise physiologic sites where NK cells mature and the mechanisms that drive the development of their functional characteristics have not yet been utterly clarified but recent studies show that these occur in the bone marrow and the lymph nodes.2 Born to kill, these cells were thought to voyage straight from the bone marrow, where they are manufactured, to the blood, circulating there and infiltrating the sites of early tumors or infectious agents in the body. Natural killer cells, as components of the innate immune system, are the first line of defense against cancerous cells and infectious agents.3 In other words; they do not desire prior exposure to the antigen to elicit a response. In fact, NK function was originally construed by the cell’s ability to kill NK-sensitive tumor cells.4
Natural killer cells can kill a ample range of cancer cells and are a promising tool for cell therapy of cancer. In the setting of the hematopoietic stem-cell transplantation, donor NK cells may employ an anti-leukemia effect if they do not express the killer-cell immunoglobulin-like receptors (KIRs) reaching with the human leucocyte antigen (HLA) class 1 epitope expresses by the patient’s leukemia cells.2 According to the journal article, “The Korean Journal of Laboratory Medicine,” in animal models, donor NK cells killed host leukemic cells and lymphohematopoietic cells without affecting non-hematopoietic tissues, suggesting the possibility of an NK-mediated graft-versus-leukemia (GVL) effect without systemic disease.2 Therefore, it is now a typical practice at some clinical centers to select donors with an HLA and KIR type that facilitates NK cell activation. However, although the results of NK-based immunotherapeutic treatment of cancer are promising in the experimental models, their clinical effectiveness in human trials has been modest. This is seemingly due to tumor avoidance by alteration of NK cell function and resistance to killing affiliated with tumor progression and chronic inflammation.5 For the future, a good control upon NK cell activity based on a deep knowledge of their primary physiology at the bench is perhaps one of the more promising tools for the management of human cancer in clinical applications.
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