How do natural killer cells defend against cancer?

Natural killer cells defend against cancer by recognising and destroying abnormal cells, including cancerous ones, without prior sensitisation.

Natural killer (NK) cells are a type of lymphocyte, a white blood cell, that plays a crucial role in the body's immune system. They are part of the innate immune system, which is the body's first line of defence against pathogens and abnormal cells. Unlike other immune cells, NK cells do not need to recognise a specific antigen before they can function. This means they can respond rapidly to a wide range of challenges.

NK cells are particularly effective at recognising and killing cells that have become cancerous. They do this through a complex process of cell recognition. Every cell in the body has proteins on its surface known as 'self' markers. These markers allow the immune system to recognise the cell as part of the body and not a foreign invader. However, when a cell becomes cancerous, it often loses these 'self' markers and may express new, abnormal ones. This makes the cancerous cell appear foreign to the immune system.

NK cells have receptors that can detect these changes. When an NK cell encounters a cell without the correct 'self' markers, it binds to it and releases cytotoxic (cell-killing) substances. These substances cause the target cell to undergo apoptosis, or programmed cell death. This effectively destroys the cancerous cell before it can divide and spread.

In addition to this direct killing, NK cells also produce chemical signals that can recruit other immune cells to the site of the cancer. They release cytokines, which are chemical messengers that stimulate other immune cells to respond. This can lead to a more robust and targeted immune response against the cancer.

However, some cancers have developed ways to evade detection by NK cells, for example by re-expressing 'self' markers or by producing substances that inhibit NK cell function. This is one reason why cancer can be so difficult to treat. Nonetheless, understanding the role of NK cells in cancer defence is leading to new strategies in cancer therapy, including treatments designed to enhance NK cell function or to make cancer cells more susceptible to NK cell attack.