<prompt> Killer cells helper cells are pa of -B cellsT cellsMonocytesMacrophages  <response>: The category of effector T cell is a broad one that includes various T cell types that actively respond to a stimulus, such as co-stimulation. This includes helper, killer, regulatory, and potentially other T cell types. Reff: Ananthanarayanan Panikers textbook of microbiology 9th edition pg: 135 