Final answer:
Reactive lymphocytes have large, dark-staining nuclei with a small rim of cytoplasm, and are crucial for the body's immune responses, including the production of antibodies and the destruction of infected or abnormal cells.
Step-by-step explanation:
Reactive lymphocytes are white blood cells characterized by several distinct nuclear characteristics. They have large nuclei that absorb Wright stain actively, leading to a dark appearance when viewed under a microscope. The nuclear morphology of lymphocytes, including Natural Killer (NK) cells, B cells, and T cells, typically shows a large nucleus occupying most of the cell's volume, with a small rim of cytoplasm around it. These cells play vital roles in the body's immune responses. NK cells, for instance, are involved in the identification and destruction of infected or abnormal cells, while B cells, upon activation, differentiate into plasma cells that can produce soluble antibodies.