Here's why:
* Nonspecific: NK cells don't need to be specifically programmed to recognize a particular antigen like T cells do. They can directly target cells showing signs of stress or abnormality.
* Tumor cells: NK cells can detect and kill tumor cells that have downregulated MHC class I expression, a common characteristic of cancer cells.
* Virus-infected cells: NK cells can recognize cells infected with viruses, particularly those that have decreased MHC class I expression or have increased expression of stress-related molecules.
Key points about NK cells:
* Part of the innate immune system: NK cells are part of the body's first line of defense, unlike T cells, which are part of the adaptive immune system.
* Granule-containing: NK cells contain cytotoxic granules that release substances like perforin and granzyme, which induce apoptosis (programmed cell death) in target cells.
* Important role in immune surveillance: NK cells constantly patrol the body for abnormal cells and eliminate them, contributing to overall immune homeostasis.
