Answer
Lymphocytes continuously cycle between lymphoid tissues, lymph and blood They spend only a few hours at a period in the blood stream. As for other white blood cells, once they leave the blood stream to deal with threats to the body by injury or infection , they never return to the blood stream.
Work Step by Step
Lymphocytes move freely from blood to lymphatic fluid to lymphoid tissue and back to blood again. Only about 2% of lymphocytes are found in the blood at any instant; the rest are the skin, lungs, lymph nodes spleen etc. Other WBCs-- neutrophils, eosinophils, monocytes-- once they leave the blood to defend the body, never return to the blood stream.
