Immunosenescence: The Effect of Aging on the Immune System

An animal’s immune function declines with age, according to H. Pendle. As animals age, "Important cell populations are not fully replenished, and eventually this affects its immune function. Important T-cell and B-cell numbers decline as these organs decline, and this has the greatest impact on the immune system. Researchers hypothesize from this that the body reallocates its energy and nutrient supplies to the less costly immune responses so that the body may use its resources for overall biologic fitness in older birds". ⁵¹