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Killer cells
7/12/12

“Today, some studies suggest that these cells can also undergo education processes and develop a form of memory. In order to recognize a cancerous cell, they also have receptors which function differently from those of the T and B lymphocytes. Therefore we can say that by their nature, they are a bridge between the two different types of immunity. They also interact with the innate immune cells to enable a better activation of the adaptive immune cells”, explains Nathalie Jacobs. It can therefore be supposed that the NK lymphocytes share characteristics of the two types of immune response.

A Balance between inhibiting and activating receptors

In order to destroy a tumor cell or a cell infected by a virus, a cytotoxic T lymphocyte must express a specific receptor on its surface which will recognize a tumor or viral antigen shown by a major histocompatibility molecule (MHC) (figure 1). However the proportion of cytotoxic T lymphocytes possessing a specific receptor for a virus or a tumor cell is very small and the lymphocyte must first proliferate due to signals given by the innate immune response in order to set off an effective response.
On the other hand an NK cell, as its name indicates, can “naturally” kill rapidly. The question is why and how?

Firstly because they already possess the molecules able to kill target cells while the T lymphocytes still have to produce them (figure 1). Theses molecules are contained in cytotoxic granules which release granzymes and perforins after interacting with the tumor cell. Perforins are proteins which, as their name indicates, perforate the membrane of the target cell. The granzymes are cytotoxic proteins which penetrate the target cell and break down its DNA to result in apoptosis or programmed cell death.

Tumor-cell-recognition-mode

All NK cells possess receptors that make it possible to potentially distinguish tumor cells (figure 1) or virally-infected cells from a normal cell.

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