Introduction

Immune senescence (a progressive dysfunctioning of the immune system) results from loss of some immunologic activities with simultaneous increase of others. Immune senescence leads to an inappropriate, inefficient, and sometimes detrimental immune response. Clinically, immune senescence has been implicated in an increasing number of age-related disorders.

Two complementary forms of immunity rid humans of pathogens and cancer cells: natural (innate) immunity and adaptive (acquired) immunity. Natural immunity provides a rapid but incomplete defense against threatening agents until the slower, more definitive adaptive immune response develops. Natural immunity has a relatively rigid structure, whereas adaptive immunity, supported by T and B lymphocytes, is infinitely versatile and adaptable. The age-related changes in cellular (T-lymphocyte-mediated) and humoral (B-lymphocyte-mediated) immunity are listed in Tables 131-1 and 131-2. Other aspects of the immune response include mucosal immunity and allergic reactivity.