NK cells are -
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
Activated macrophages
Antibody-activated T cells
Null cells activated by complement
Independent of antibody
Immunology