We've got to get beyond the knee-jerk reaction that LASIK isn't appropriate for any patient under 18 years of age, said Davidorf. The subtext is that Hahn wanted to get rid of the embarrassment of airport officials' knee-jerk reaction that it's OK to snub the Valley by trampling on one of its beloved traditions.
Natural killer cells, or NK cells, are a component of the innate immune system which does not directly attack invading microbes. Rather, NK cells destroy compromised host cells, such as tumor cells or virus-infected cells, recognizing such cells by a condition known as missing self..
These three types of leukocytes are even further divided into more specialized cells, each with their own unique task in the immune system. To learn more details about the immune system, see Additional Resources. How does your immune system know which cells to attack and which cells are part of your own body? Your immune system can recognize cells based on the proteins present on the surface of cells. Viruses, bacteria, and other foreign cells are recognized as being different from your own cells and are attacked by your immune system. Sometimes, one of your own cells changes, or mutates, giving the cell the ability to multiply continuously. Such mutations often are the cause of cancer.