The human defense system consists of factors that provide innate and acquired immunity against microorganisms. The system evolved from primitive but effective defenses found in more ancient animal species. The innate defenses include 1) structural barriers, 2) acids, bases, and other chemical agents produced at various sites, such as mucosal surfaces, and 3) highly phagocytic, motile scavenger cells that have well-developed killing and digestive powers. As a result of the evolutionary process, the mammalian immune system has become more specific, efficient, regulated, and complex. The development of specialized innate and acquired recognition/regulatory proteins (antibodies, cell receptors, and cytokines) expanded the repertoire, and control the magnitude of the protective responses. One of the most important consequences of this evolution is the ability of the immune system to discriminate between self and non-self antigens and maintain a memory of previous encounters with antigens, including those from microorganisms.
The evolutionary changes allowed development of B and T cells which express antigen-specific receptors on their cell surface. These changes permit humans to survive in an environment laden with microbial pathogens and environmental toxins. The pathogenic features of those microorganisms include the ability to 1) enter the body through portals such as the skin, respiratory system, and the alimentary tract; 2) utilize nutrients from those sites; 3) adhere to epithelium; 4) produce virulence factors and toxins; 5) commandeer the replicative machinery of the host's cells; 6) evade the immunologic system; 7) cripple the defenses of the host; and 8) cause autoimmune responses by acting as cross-reactive antigens.
The salient features of the human defense system that evolved to counteract the pathogenic microorganisms and prevent autoimmune problems will be presented in the rest of this chapter.
The evolutionary changes allowed development of B and T cells which express antigen-specific receptors on their cell surface. These changes permit humans to survive in an environment laden with microbial pathogens and environmental toxins. The pathogenic features of those microorganisms include the ability to 1) enter the body through portals such as the skin, respiratory system, and the alimentary tract; 2) utilize nutrients from those sites; 3) adhere to epithelium; 4) produce virulence factors and toxins; 5) commandeer the replicative machinery of the host's cells; 6) evade the immunologic system; 7) cripple the defenses of the host; and 8) cause autoimmune responses by acting as cross-reactive antigens.
The salient features of the human defense system that evolved to counteract the pathogenic microorganisms and prevent autoimmune problems will be presented in the rest of this chapter.