Lymphocytes Are Responsible for Acquired Immunity
Acquired immunity is the product of the body’s lymphocytes. In people who have a genetic lack of lymphocytes or whose lymphocytes have been destroyed by radiation or chemicals, no acquired immunity can develop. And within days after birth, such a person dies of fulminating bacterial infection unless treated by heroic measures. Therefore, it is clear that the lymphocytes are essential to survival of the human being. The lymphocytes are located most extensively in the lymph nodes, but they are also found in special lymphoid tissues such as the spleen, submucosal areas of the gastrointestinal tract, thymus, and bone marrow. The lymphoid tissue is distributed advantageously in the body to intercept invading organisms or toxins before they can spread too widely. In most instances, the invading agent first enters the tissue fluids and then is carried by way of lymph vessels to the lymph node or other lymphoid tissue. For instance, the lymphoid tissue of the gastrointestinal walls is exposed immediately to antigens invading from the gut. The lymphoid tissue of the throat and pharynx (the tonsils and adenoids) is well located to intercept antigens that enter by way of the upper respiratory tract. The lymphoid tissue in the lymph nodes is exposed to antigens that invade the peripheral tissues of the body. And, finally, the lymphoid tissue of the spleen, thymus, and bone marrow plays the specific role of intercepting antigenic agents that have succeeded in reaching the circulating blood.