Natural killer cells are white blood cells that defend against foreign invaders such as tumors, bacteria, and viruses by recognizing human leukocyte antigens (HLA) on the surface of other cells. If the HLA appears foreign, the natural killer cell will release toxins that kill the foreign cell. However, the body has steps in place to prevent natural killer cells from attacking their host.
A natural killer or NK cell is a white blood cell that acts as the immune system’s first line of defense against foreign invaders such as tumors, bacteria, and viruses. NK cells are known as “natural killers” because they don’t need to react to specific antigens, they just need to recognize that a cell is foreign and doesn’t belong to them. Because these cells are so powerful, the body has a number of steps in place designed to keep NK cells from ramping up and accidentally attacking their host.
To understand how natural killer cells work, it is necessary to take a brief foray into biology. These cells look for proteins known as human leukocyte antigens (HLA) that show up on the surface of other cells. If a natural killer cell recognizes HLA proteins as belonging to “itself”, it ignores the cell, assuming it belongs. If, however, the HLAs appear foreign, the natural killer cell will release toxins that kill the foreign cell.
HLAs are expressed through the Major Histocompatibility Complex, a group of genes located on the sixth chromosome. The Major Histocompatibility Complex is “major” because it plays a critical role in the acceptance or rejection of transplanted tissues. If the HLAs on an organ don’t match, the body will reject it, with natural killer cells moving in to protect the body from a perceived invader.
A natural killer cell has a number of receptors that it uses to gather information about the cells it contacts. Typically, at least one specific receptor must be activated for a natural killer cell to act. Other cells of the immune system may also be involved in the response, with the immune system leaping into action to address emerging health problems. The natural killer cell works by attaching itself to the suspect cell and essentially injecting it with cytotoxins, substances designed to kill cells.
Sometimes, things go wrong with natural killer cells. For example, sometimes a woman carries a baby with incompatible HLAs and natural killer cells think the fetus is dangerous. In these cases, various medical treatments are used with the aim of allowing the baby to develop so that the woman can carry the baby to term. Natural killer cells can also become malignant, developing into lymphoma, a type of cancer. NK cell lymphoma can be extremely difficult to treat.
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