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Title: IMMUNITY: ACQUIRED

Author
item Lunney, Joan
item Paape, Max
item Bannerman, Douglas

Submitted to: Encyclopedia of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2003
Publication Date: 11/10/2004
Citation: Lunney, J.K., Paape, M.J., Bannerman, D.D. 2004. Immunity: acquired. In:Encyclopedia of Animal Science. W.G. bond and A.W. Bell, editors. Marcel Dekker, New York. pp. 548-551.

Interpretive Summary: Knowledge of the immune response is needed for many aspects of animal science and animal health research. This article updates the reader on current areas of importance in immunology, addressing specifically acquired, or adaptive, immune responses. These are responses dominated by immune cell interactions and resultant production of immune regulatory proteins (e.g., chemokines, cytokines and antibodies, or immunoglobulins). To promote acquired immune responses there must be interactions between key immune cells, T lymphocytes, B lymphocytes, macrophages, dendritic cells, or other antigen presenting cells (APC). To activate acquired immunity foreign antigens (i.e., the products derived from infectious organisms, tumors, vaccines, etc.) must be processed and immune responses initiated, resulting in final antigen specific responses. Some T cells respond to intracellular infections and are called T helper 1 (Th1) cells; others respond to extracellular infections and allergens and are called (Th2) cells. Th1 and Th2 cells produce different immune cytokines that either stimulate, or prevent, immune responses. Subsets of T and B cells modify their surface T and B cell receptors as they respond to each antigen. T cell subsets later provide memory, such as is found with vaccinations, where months later an active, acquired antibody or cytokine response helps the vaccinated animal prevent an infection that might otherwise cause morbidity or even mortality. Acquired immune responses ultimately determine whether an infectious organism will be controlled and disease presented. Thus, knowledge of acquired immunity is essential as scientists plan new controls for infectious diseases.

Technical Abstract: Higher species have the evolutionary benefit of an immune system that is comprised of both innate and acquired components. Whereas the innate immune system confers initial protection, the acquired immune system provides a second line of defence against infectious organisms. The acquired immune system is activated once macrophages, dendritic cells, and other 'antigen presenting cells (APC)' process foreign antigens (i.e., the products derived from infectious organisms, tumors, vaccines, etc.) Many APC also transport the foreign antigen into regional immune lymph nodes. APCs initiate adaptive immune responses by interacting with different populations of T and B cells. This manuscript outlines the differences between the innate and adaptive, or acquired, immune responses and the critical roles of immune cell subsets and their products in acquired immunity. It outlines how the animal host responds when invaded by foreign agents and initiates cell-mediated responses, either a T helper 1 (Th1) response to intracellular infections or Th2 response to extracellular infections and allergens. The invading organism determines which type of response dominates. These responses are regulated by hormone-like proteins called cytokines, which are secreted by immune cells, and can activate or suppress the activity for each type of response. Acquired immune responses ultimately determine whether an infectious organism will be controlled and disease prevented. Vaccines enhance immunity by altering the acquired immune response. Much research is now aimed at biotherapeutics that alter the balance between Th1 and Th2 cytokine responses. Since cytokines set the direction and amplify the intensity of specific anti-pathogen and vaccine immune responses, setting the direction of the early specific acquired immune response will help determine whether effective immunity will develop. Indeed, the ability to turn cytokine responses on and off quickly, will determine how efficiently an animal controls the infection process.