what cells in the blood help defend against infection?
White blood cell. White blood cells (also called leukocytes or immune cells) are cells which form a component of the blood. They help to defend the body against infectious disease and foreign materials as part of the immune system. There are normally between 4x109 and 11x109 white blood cells in a litre of healthy adult blood - about 7,000 to 25,000 white blood cells per drop.