Innate Immunity

Adaptive immunity mediated by antigen-specific T and B lymphocytes is essential for the survival of all mammals and most other vertebrates, but a wide variety of other mechanisms independent of antigen recognition by the specific receptors of T and B cells are also involved in successful immune protection. These diverse mechanisms are collectively known as innate immunity because they are innately present from birth and do not depend on prior exposure to specific pathogens for their amplification. Such responses are controlled by the products of germline genes that are inherited and similarly expressed by most or all healthy people. Innate immune mechanisms involve both constitutive and inducible components and use a wide variety of recognition and effector mechanisms. Multiple pathways by which pathogens can be detected by germline-encoded receptors have been identified, many involving receptors with leucine-rich repeat domains such as Toll-like receptors (TLRs) and Nod-like receptors (NLRs). It is now recognized that innate immune responses have a profound influence on the generation and outcome of adaptive immune responses. The innate immune system has a major role in instructing the responses of the adaptive immune system, indicating many ways in which innate immunity influences the development of both long-term specific immunity and autoimmune disease.