Natural killer cell - Innate Immunity

 Natural killer cell

Natural killer (NK) cells are a type of cytotoxic lymphocyte that plays a critical role in the innate immune response against infected or cancerous cells. They are a subset of white blood cells known as lymphocytes and are part of the body's first line of defense against pathogens and tumor cells.

Here are some key features of natural killer cells:

1. Function: NK cells are responsible for detecting and killing abnormal cells, including virus-infected cells and tumor cells. They recognize and destroy these target cells without prior sensitization or activation.

2. Innate Immunity: NK cells are considered part of the innate immune system because their activity does not require prior exposure or specific recognition of antigens. They can quickly respond to abnormal cells through a variety of activating and inhibitory receptors on their surface.

3. Recognition: NK cells have surface receptors that can detect the absence or alteration of self-molecules, which are usually displayed on the surface of healthy cells. This allows NK cells to distinguish between normal and abnormal cells.

4. Activating and Inhibitory Receptors: NK cells express both activating and inhibitory receptors. The balance between these signals determines the activation or inhibition of NK cell responses. The inhibitory receptors recognize self-molecules, while activating receptors recognize stress-induced molecules or viral proteins on target cells.

5. Killing Mechanisms: Once activated, NK cells use several mechanisms to kill target cells. They can release cytotoxic granules containing perforin and granzymes, inducing apoptosis (cell death) in the target cells. NK cells can also induce target cell death through the expression of death receptor ligands.

6. Immunoregulatory Functions: NK cells also play a role in modulating the adaptive immune response. They can produce cytokines and chemokines that influence the activity of other immune cells, such as macrophages and dendritic cells.

NK cells are an essential component of the immune system's surveillance against infected and cancerous cells. Their ability to recognize and eliminate abnormal cells without prior sensitization makes them a critical defense mechanism in the body. Researchers continue to study NK cells to understand their functions better and explore their potential in immunotherapies for various diseases, including cancer.