Welcome to the next lecture in Leaning Unit 3 where you will learn about the importance of nutrients in animal life I am Dr Peter Ferket and this lecture is about nutrition and immunity in animals In learning unit 2 you learned some basic concepts of nutrients affect growth maintenance and metabolism In this lecture we will discuss how these nutrients function in maintaining health and immunity 1 Nutrition has an impact on every physiological process in the body So it should not be sur prising that nutrition also has important implica tions on immunity and incidence of disease for humans and animals While scientists have known for many years that nutrition influences immunity only in recent years have some of the specific mechanisms by which nutrients affect immunity become apparent Of course nutrients affect metabolism but the immune system often has metabolic priority when challenged with immunological stress causing nutrients to be diverted away from productive purposes such as growth reproduction and maintenance Immune system cells and tissues have particularly unique nutritional requirements and when activated may have different demands for specific nutrients that other body tissues need The diet also can impact the enteric microbiome which interact with gut associated immune system 2 The gut microbiota or the microbiome has unique functions to support gut health and immune function Indeed it is commonly said there are more cells associated with the enteric microbiome than all the cells in the host animal So when we are feeding an animal we are not really feeding the animal but the whole ecosystem that is in and part of the animal The gut microbiota has a metabolic function They complete with the host for dietary compounds or use host secretions to produce organic acids vitamins and other metabolites some of which benefit the host The microbiota have a protective function as beneficial microbiota displace pathogens or produce antimicrobial factors They also have an immunological function and are important for immune system development especially in juvenile animals 3 3 Indeed the intestinal microbiota can profoundly affect the activation of both innate and adaptive immunity at the local level in the mucusa lamina propria Peyer s patches and mesenteric lymph nodes This illustration from Li et al 2022 summarizes how the gut microbiome can affect host immunity and what modulates the gut microbiome is the animal s diet I don t intend to go into the details of how the microbiome specifically affects host immunity but simply to illustrate the potential implications of diet and microbiome modulation can influence systemic 4 immunity as the gut is the primary interface with the potential antigens outside the body You can read the review paper sited on the bottom this slide for more details 4 The immune system can be generally separated into three broad components 1 natural immunity 2 innate immunity and 3 acquired immunity All of these immune function components must be fully developed and functioning properly to provide adequate immunological protection Natural and innate immunity are typically grouped together under the category of innate immunity So what is innate immunity The innate immune system is an evolutionarily ancient mechanism to fight disease and represents the antigen non specific defense mechanisms of the immune system that is elicited immediately or within several hours 0 4 h after exposure to an antigen It consists of several anatomic physiologic and cellular components Anatomic aspects include the epithelial barriers to infection provided by the skin lung mammary and gastrointestinal tract Secretion of hydrochloric acid and digestive enzymes by the gastrointestinal tract also aids in preventing entry of pathogens into the body Remember when we talked about the very low stomach pH of vultures Vultures eat carcasses dead rotting animal flesh the rotting is of course due to the decay by microorganisms some of which could be pathogenic So that low pH is a mechanism to protect the vultures from infection from the microbes they consume when eating dead animals in addition to the role it plays in the breakdown of proteins as discussed in earlier lectures 6 Innate immunity is a non selective immune sys tem It is not an antigen specific immune response as it does not modify itself depending on the type of pathogen challenge Instead it prevents infection by targeting general properties of pathogens For example few pathogens can withstand the low pH of the stomach abomasum and most should be digested by the digestive enzymes of the gastrointestinal tract In fact the majority of organisms encountered by an animal on a daily basis do not cause disease under normal circumstances as they are readily detected and eliminated by the innate immune system 7 The complement system is a component of innate immunity but it can recruit and bring into action antibodies generated by the adaptive immune system But in addition of these animals possess a cellular component of innate immunity The illustration in the upper right shows the classical and alternative pathway of the complement cascade showing how an antigen and antibody C1 complex initiates a cascade of subsequent complex responses to ultimately destroy the pathogenic cell Animals also possess a cellular component of innate immunity which consists of phagocytic cells such as neutrophils and macrophages that are activated at sites of infection and then attack and kill pathogens before pathogens have the opportunity to proliferate and cause a significant infection 8 The second wall of protection is the acquired or adaptive immunity The adaptive immune system and is characterized by production of antibodies that are directed against specific antigens The use of vaccines to protect animals from various pathogens is an example of acquired immunity Acquired immunity can be classified as either cell mediated immunity or humoral immunity Cell mediated immunity represents the immunological response associated with immune cells that act directly against pathogen infected cells Humoral immunity involves the generation of specific antibodies that are directed against the invading pathogens 9 This graphic illustrates the difference between innate and adaptive immunity The innate immunity involves dendritic cells mast cells macrophage natural killer cells basophils eosinophils neutrophils granulocytes and complement protein In contrast adaptive