Adaptive immunity in the liver

Abstract

Whereas innate immunity can provide the initial defense against infections, completely effective immunity to an invading microbial organism typically requires an adaptive immune response specific to the invader. Adaptive immune responses in the liver contribute both to effective defense against invading microbes and to a variety of pathologic states. The term adaptive immunity refers to lymphocyte-mediated immune defense tailored to a specific microbial invader. Adaptive immunity can be classified into humoral immunity and cell-mediated immunity, mediated principally by B and T lymphocytes, respectively. Antigens are structures found on microbes that are recognized as foreign by B or T lymphocytes. Antigens elicit specific responses from the lymphocytes expressing cognate antigen receptors. Such specific responses include both clonal proliferation and lymphocyte differentiation into specialized effector cell types with important functions serving to fight microbes. Such functions include the release of antibody (B cells), the killing of infected cells (cytotoxic T cells), and extracellular release of signaling molecules (i.e., cytokines) that can act in an autocrine, paracrine, or endocrine fashion to elicit responses from other immune and nonimmune cells. © 2007 Humana Press Inc.