Final answer:
Natural killer cells (c) are an element of the innate immune system, providing a non-specific defence against pathogens and infected or cancerous cells without previous exposure or memory activation.
Step-by-step explanation:
An element of the innate immune system that the student asked about is natural killer cells (c). Unlike T cells and B cells, which are part of the adaptive immune system and provide a specific response to pathogens, natural killer cells are a non-specific defence mechanism that helps to protect the body from infection. They work by recognizing and destroying cells that have been compromised by a virus or have become cancerous without the need for prior exposure or the development of memory cells.
Natural killer cells are a critical part of the immune system as they can respond immediately to a wide range of challenges without the delay that is characteristic of the adaptive immune response. This rapid response is an important first line of defence against infectious agents.