NK cells are -: (A) Activated macrophages, (B) Antibody-activated T cells, (C) Null cells activated by complement, (D) Independent of antibody
Answer is D. NK cells are unique, however, as they have the ability to recognize stressed cells in the absence of antibodies and MHC, allowing for a much faster immune reaction. They were named "natural killers" because of the initial notion that they do not require activation to kill cells that are missing "self" markers of MHC class 1. Reff: Ananthanarayanan & Panikers textbook of microbiology 9th edition pg:137