20: Innate Immunity 1
- Last updated
- Apr 18, 2025
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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 chapter, and specific adaptive host defenses, which are discussed in the next chapter.
The nonspecific innate immune response provides a first line of 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. 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 - 20.1: Physical Defenses Overview
- This page explains nonspecific innate immunity and its diverse defenses against infections, including physical barriers such as skin, mechanical actions that eliminate microbes, and the microbiome's role. It emphasizes the importance of these overlapping defenses in preventing pathogen entry and maintaining health, underscoring innate immunity's essential role as the first line of defense against diseases.
- 20.2: Physical Barreirs - Skin and Mucous Membranes
- This page discusses the significance of physical barriers, such as skin, mucous membranes, and endothelia, in preventing microbial infections. It highlights the skin's layers, mucous membranes' role in trapping pathogens, and the protective function of endothelial cells in the blood-brain barrier. These components are part of the body's innate immunity, crucial for removing microbes and maintaining sterility in sensitive areas.
- 20.3: Chemical Defenses - Overview
- Numerous chemical mediators produced endogenously and exogenously exhibit nonspecific antimicrobial functions. Many chemical mediators are found in body fluids such as sebum, saliva, mucus, gastric and intestinal fluids, urine, tears, cerumen, and vaginal secretions. Antimicrobial peptides (AMPs) found on the skin and in other areas of the body are largely produced in response to the presence of pathogens. These include dermcidin, cathelicidin, defensins, histatins, and bacteriocins.
- 20.4: Chemical Defenses - Antimicrobial Peptides (AMP) and Plasma Protein Mediators
- This page discusses antimicrobial peptides (AMPs), such as defensins and bacteriocins, which possess broad-spectrum properties against microorganisms. It highlights their various mechanisms of action against bacteria, fungi, and viruses. Additionally, it mentions antimicrobial proteins in plasma, particularly acute-phase proteins like C-reactive protein and ferritin, which are vital for the innate immune response and aid in inhibiting pathogen growth and promoting phagocytosis.
- 20.5: Chemical Defenses - Complement System
- This page discusses the complement system, a collection of over 30 plasma proteins involved in both innate and adaptive immunity. It can be activated via three pathways: alternative, classical, and lectin, culminating in the activation of complement protein C3, leading to C3a and C3b production.
- 20.6: Chemical Defenses - Cytokines
- This page describes cytokines as soluble proteins facilitating communication in the immune system, influencing cell proliferation and apoptosis. They operate through autocrine, paracrine, or endocrine signaling. Key classes include interleukins, chemokines, and interferons, each playing specific roles in immune modulation and infection response.
