Unit 8.1: Innate Immunity
Outline
- Chemical and Enzymatic Mediators Found in Body Fluids
- Antimicrobial Peptides
- Plasma Protein Mediators
Learning Objectives
After reading the following, you should be able to:
- Define innate immunity and adaptive immunity.
- Differentiate between the first and second lines of defense.
- Differentiate between physical versus chemical factors in the first line of defense.
- Describe the role of the normal flora in the innate immunity.
- Describe the role of the following components of the second line of defense:
- Immune cells (including Mast cells, Natural killer cells and Phagocytes)
- Phagocytosis (identify which cells are phagocytes and be able to describe the stages)
- Inflammation (signs, functions and stages)
- Fever (mechanism and advantages to host)
- Antimicrobial substances
- Describe and give an example of cytokines important to the innate immune system.
- Describe how pathogens can resist death by phagocytosis.
- Describe how bacteria can evade complement system.
- Describe why interferons can be used as a drug and describe the issues that come with using interferons as a drug.
Despite relatively constant exposure to pathogenic microbes in the environment, humans do not generally suffer from constant infection or disease. Under most circumstances, the body is able to defend itself from the threat of infection thanks to a complex immune system designed to repel, kill, and expel disease-causing invaders. Immunity as a whole can be described as two interrelated parts: nonspecific innate immunity, which is the subject of this section, and specific adaptive host defenses, which are discussed in the next section.
The nonspecific innate immune response provides an initial defense that can often prevent infections from gaining a solid foothold in the body. These defenses are described as nonspecific because they do not target any specific pathogen; rather, they defend against a wide range of potential pathogens. They are called innate because they are built-in mechanisms of the human organism. Unlike the specific adaptive defenses, they are not acquired over time and they have no “memory” (they do not improve after repeated exposures to specific pathogens).
Broadly speaking, nonspecific innate defenses provide an immediate (or very rapid) response against potential pathogens. The innate immune response can roughly be separated into two divisions, the first line and second line of defense. The first line of defense involves preventing pathogens from gaining access to the body and includes features such as the skin and mucous membranes. The second line of defense comes into play when pathogens are able to bypass these initial barriers and includes chemical and cellular responses. However, these responses are neither perfect nor impenetrable. They can be circumvented by pathogens on occasion, and sometimes they can even cause damage to the body, contributing to the signs and symptoms of infection (Figure 8.1