Natural killer (NK) cells are a type of lymphocyte that play a crucial role in the innate immune system. They are called 'natural' because they can rapidly respond to and destroy infected or cancerous cells without prior sensitization or activation, unlike other lymphocytes like T cells and B cells.
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NK cells are a type of lymphocyte that are part of the innate immune system, providing a rapid first line of defense against infections and cancer.
NK cells can recognize and kill infected or transformed (cancerous) cells without prior sensitization, unlike T cells and B cells of the adaptive immune system.
NK cells use a variety of activating and inhibitory receptors to recognize and respond to changes in cells, such as the downregulation of MHC class I molecules.
Upon activation, NK cells release cytotoxic granules containing perforin and granzymes, which induce apoptosis (programmed cell death) in the target cell.
NK cells also play a role in antibody-dependent cell-mediated cytotoxicity (ADCC), where they use their Fc receptors to bind to antibodies attached to target cells, triggering their destruction.
Review Questions
Explain the role of natural killer (NK) cells in the innate immune system.
Natural killer (NK) cells are a crucial component of the innate immune system, providing a rapid and immediate response to infected or transformed (cancerous) cells. Unlike adaptive immune cells like T cells and B cells, NK cells do not require prior sensitization or activation to recognize and destroy target cells. They use a variety of activating and inhibitory receptors to detect changes in cells, such as the downregulation of MHC class I molecules, which can indicate that a cell has been infected or transformed. Upon activation, NK cells release cytotoxic granules containing perforin and granzymes, which induce apoptosis (programmed cell death) in the target cell, effectively eliminating the threat.
Describe the mechanism by which natural killer (NK) cells can induce cell death in target cells.
Natural killer (NK) cells have the ability to induce cytotoxicity, or cell death, in target cells through two primary mechanisms. First, upon activation, NK cells release cytotoxic granules containing perforin and granzymes. Perforin forms pores in the target cell membrane, allowing the granzymes to enter the cell and activate apoptotic pathways, leading to programmed cell death. Second, NK cells can also engage in antibody-dependent cell-mediated cytotoxicity (ADCC), where they use their Fc receptors to bind to antibodies attached to target cells. This binding triggers the release of cytotoxic granules and the destruction of the target cell. Through these cytotoxic mechanisms, NK cells play a crucial role in the innate immune system's defense against infections and cancer.
Analyze the significance of natural killer (NK) cells in the overall immune response, particularly in comparison to other lymphocytes like T cells and B cells.
Natural killer (NK) cells occupy a unique and important position in the immune system, as they provide a rapid, first-line defense against infections and cancer, unlike the adaptive immune cells like T cells and B cells. While T cells and B cells require prior sensitization and activation to mount a specific response, NK cells can immediately recognize and destroy infected or transformed cells without this prerequisite. This immediate cytotoxic capability makes NK cells crucial in the innate immune response, as they can quickly eliminate threats before the adaptive immune system has time to generate a targeted response. Additionally, NK cells play a role in antibody-dependent cell-mediated cytotoxicity, allowing them to collaborate with the adaptive immune system to enhance the overall immune response. The ability of NK cells to bridge the gap between innate and adaptive immunity highlights their significant contribution to the body's comprehensive defense against disease and malignancy.
The body's first line of defense against pathogens, which includes physical barriers, chemical defenses, and immune cells like NK cells that respond immediately to threats.
The ability of certain immune cells, including NK cells, to induce cell death in target cells through the release of cytotoxic granules or the activation of apoptotic pathways.
A process where NK cells use their Fc receptors to bind to antibodies attached to target cells, triggering the release of cytotoxic granules and the destruction of the target cell.