How do Natural Killer cells contribute to the immune response?

Natural Killer (NK) cells play a critical role in the immune response primarily by directly killing infected or cancerous cells. This cytotoxic capability is a major part of the innate immune response, which acts quickly to eliminate threats such as virus-infected cells and tumors. NK cells recognize stressed or abnormal cells without the need for prior sensitization to a specific pathogen.

Once NK cells identify their targets, they release cytotoxic granules containing perforin, which creates pores in the target cell membrane, and granzymes, which are enzymes that induce apoptosis (programmed cell death) in the infected or cancerous cells. This direct killing action is essential for controlling viral infections and limiting the spread of tumors in the body.

The other processes mentioned, such as producing antibodies (primarily done by B cells), enhancing phagocytosis (which relies on cells like macrophages and neutrophils), and activating helper T-cells (performed mainly by antigen-presenting cells), emphasize different roles in the immune system but are not the primary function of NK cells. Thus, their defining contribution lies in their ability to directly attack and eliminate compromised cells, safeguarding the body against infections and malignancies.