Adaptive immunity - The basics

Authors: Carroll, Jeffery - Jeff Carroll

Submitted to: American Dairy Science Association Discover Conference
Publication Type: Proceedings
Publication Acceptance Date: 10/16/2019
Publication Date: 10/28/2019
Citation: Carroll, J.A. 2019. Adaptive immunity - The basics. American Dairy Science Association Discover Conference. p. 1-6. Itasca, IL, October 28-31, 2019.

Interpretive Summary: It has been well-established that an animal’s ability to protect itself from diseases and other immunological challenges within its environment depends upon the presence of a well developed and properly functioning immune system. It is also common knowledge that animals which possess an adequate level of immunological protection have greater reproductive capabilities, enhanced growth, and increased feed efficiency. However, even animals that have an immune system functioning at an optimum level can often become susceptible to disease following exposure to various stressful conditions such as extreme fluctuations in environmental temperature, poor or inadequate nutrition, improper handling techniques, mixing of unfamiliar animals, inadequate ventilation, and unsanitary housing conditions. As researchers continue to explore the complex interactions among stress and production parameters such as growth, reproduction, and health, multidisciplinary efforts are leading to a greater understanding of the importance of a properly functioning immune system. Therefore, basic information pertaining to understanding aspects of the immune system in livestock will be presented. The information provided will be of interest to scientists, veterinarians and producers who are involved in livestock health.

Technical Abstract: There are three basic components of the immune system; natural immunity, innate immunity, and adaptive/acquired immunity. These components work independently as well as synergistically with each other to ensure an adequate immunological protection within an individual. Typically, natural and innate immunity are discussed together as a single entity under the category of innate immunity. The natural immune response serves as the first line of defense while the innate immune response serves as the second line of defense against pathogens via antimicrobial responses. However, in the event the innate immune system is unable to eliminate the invading pathogens, it controls pathogen progression and signals for the initiation of an “adaptive” immunological response. The adaptive immune response is initiated through a variety of cellular activities such as antigen presentation and chemical messenger signaling pathways and represents the arm of the immune system that “adapts” and builds a specific immune response for each unique antigen it encounters. The adaptive immune response possesses “immunological memory” which allows subsequent exposures to the same pathogens to elicit faster and stronger immune responses than that associated with the original pathogen exposure (Janeway et al., 2005). The use of vaccines to provide immunological protection against subsequent exposure to the same pathogen is an example of the “adaptive” component of the immune system. In general, the adaptive immune system can be classified as either cell-mediated or humoral immunity and is characterized by the production of antibodies which are directed against specific antigens. Adaptive immunity requires the involvement of specialized white blood cells (T and B lymphocytes), various cytokines, and antibodies to provide long-term immunological protection. Cell-mediated immunity represents the immunological responses associated with immune cells (i.e., T lymphocytes) that directly attack antigen-bearing cells and destroy them using selective chemicals. Humoral immunity on the other hand involves the B lymphocytes that generate specific antibodies that are directed against the invading pathogens. Adaptive immunity can be further categorized as either passive or active immunity. Passive immunity refers to the maternal immunity that newborns acquire primarily through colostrum from their dam during the first few days of life. For many animals, this passive immunity is very important to survival given their relatively immature immune systems early in life. The length of immunological protection from passive immunity is limited and will depend upon the concentration of antibodies the newborn received and absorbed from the colostrum, and how fast the antibodies are degraded. After the maternal antibodies have disappeared, the immune system of the offspring must become “active” (i.e., adaptive immunity) and be able to mobilize the necessary immune cells and produce the necessary antibodies to provide immunological protection from invading pathogens throughout its life.