Cell that becomes active in response to stimulation. In immunology, a differentiated lymphocyte capable of mounting a specific immune response, e.g., antibody production, lymphokine production or helper, suppressor, or killer function. Called also effector lymphocyte.
A cell that performs a specific function in response to a stimulus; usually used to describe cells in the immune system.
An active cell of the immune system responsible for destroying or controlling foreign antigens.