Chapters
3
Overview
The human body is awash in a sea of microbes. To prevent invasion by foreign pathogens and/or ‘non-self’, the body has evolved complementary and overlapping defense mechanisms, or barriers, as depicted below (Figure 35).
Figure 35: Barriers against pathogens and non-self
The defense mechanisms to pathogens and non-self include:
- Physical barriers
- Inflammatory response
- Innate and acquired immune responses
In a nutshell, the function of these defense mechanisms is to preserve homeostasis by protecting the body from ‘non-self’, or any material which may be considered foreign to the body and which may cause disease. Non-self can include microbial pathogens, organic molecules such as proteins, as well as non-organic material such as asbestos or coal dust. Non-self can also extend to cancerous cells and those transformed by viruses. In this unit, we will discuss each mechanism separately, although as alluded to above, each of these systems to varying degrees overlap functionally and physically. By the end of this unit, you should have a clear understanding of the overall function of the mechanisms protecting the human body from non-self. Disordered function of any one of these systems can result in pathology, and we will discuss specific examples of disease states that result from either hyper- or hypo-functioning defense mechanisms.
Learning Outcomes
Completion of this chapter’s readings and learning activities will enable you to:
3.1: Discuss physical barriers which prevent the entry of ‘non-self’
3.2: Understand the signs, symptoms, and effectors of the inflammatory response
3.3 Describe the cellular and humoral effectors of the innate immune response
3.4: Describe the cellular and humoral effectors of the acquired (adaptive) immune response
3.5 Distinguish between hypersensitivity reactions, autoimmunity, and immune deficiencies
Key Concepts
- Physical barriers are first line of defense
- The inflammatory response is primarily a vascular process that has evolved to isolate microorganisms
- Cytokines regulate inflammatory and immune responses, and include interleukins and interferons
- The inflammatory and innate immune response are rapid, relatively non-specific defense mechanisms against ‘non-self’
- Toll-like receptors (TLRs) are pattern recognition molecules which facilitate the recognition of bacterial and viral pathogens, as well as molecules released by damaged cells
- The acquired or adaptive immune response utilizes antibodies, MHC II receptors and T cell receptors to recognize specific pathogens
- B cells synthesize antibodies
- Antigen presenting cells are part of the innate and acquired immune responses, and include dendritic cells, Langerhans cells, and B cells
- T cells include several subclasses which help regulate the acquired immune response
- Hypersensitivity reactions are exaggerated responses to either self or non-self molecules
Learning Units
Unit 3.2 The Inflammatory Response
Unit 3.3 The Innate Immune