Chapter 1. Chapter 31: Immune System

1.1 Introduction

Welcome to the Interactive Study Guide for Chapter 31: Immune System! This Study Guide will help you master your understanding of the chapter's Driving Questions, using interactive Infographics and activities, as well as targeted assessment questions. Click "Next" to get started, or select a Driving Question from the drop-down menu to the right.

DRIVING QUESTIONS

• What is the structure of a virus, and how do viruses cause disease?
• What is innate immunity?
• What is adaptive immunity, and how does vaccination rely on it?
• What specific features of influenza virus allow it to cause worldwide outbreaks?

1.2 Driving Question 1:

Why should you care?

Viruses cause diseases ranging in severity from the common cold to Ebola. Some, like the common cold virus, cause disease symptoms shortly after infection. Others, like HIV, can remain dormant for long periods before beginning to affect the host. With many viruses, recovery happens relatively quickly as the immune system gets rid of the invaders. Others, like the herpesvirus that causes cold sores or the varicella virus that causes chicken pox in children and the painful condition known as shingles in adults, cause latent infections: the virus is never eliminated but goes through periods of dormancy and activity for reasons that are not clearly understood. Viral diseases are difficult to treat; understanding how viruses infect and replicate in their host cells can help you understand why.

What should you know?

To fully answer this Driving Question, you should be able to:

1. Diagram a typical virus.
2. Diagram and describe the general process of viral infection and replication.
3. Explain how replicating viruses can kill host cells.

Infographic Focus

The Infographics most pertinent to the Driving Question are 31.1 and 31.2.

Diagram a typical virus.

1.

In your notebook, diagram a virus, indicating its major components.

Diagram and describe the general process of viral infection and replication.

2.

Describe the process of viral infection and replication (in essay or list form) by incorporating each key process (numbered orange boxes) and structure (lettered orange arrows) into your answer.

1.3 Driving Question 2:

Why should you care?

Most of us think of white blood cells and antibodies when we think of how we avoid infection, however, natural selection has led to a much more comprehensive defensive system, one that includes both rapid, nonspecific defenses (innate immunity) and slower but highly specific defenses (adaptive immunity). Between these two systems, a very large number of pathogens are defeated even before they make us ill; many more make us uncomfortable for a short time but do no long-term damage.

You know that exposure to pollen makes your eyes and nose runny. You know that mosquito bites and scratches leave red, hot, swollen marks on your skin. You know that your stomach fluid is acidic, and you may know that your saliva is as well. What you may not know is why. In fact, all of these are instances of your innate immune system protecting you from foreign invaders.

What should you know?

To fully answer this Driving Question, you should be able to:

1. Describe the role of physical barriers in innate immunity.
2. Describe the inflammatory process and its role in innate immunity.
3. List the two types of phagocytes and describe their role in innate immunity.
4. List three body fluids containing antimicrobial chemicals, explain the chemicals’ effect on pathogens, and describe their roles in innate immunity.
5. Describe the role of complement proteins in innate immunity.
6. Explain why each of these defense mechanisms is considered part of innate rather than adaptive immunity.

Infographic Focus

The Infographics most pertinent to the Driving Question are 31.3 and 31.4.

1.4 Driving Question 3:

Why should you care?

Many infectious agents have adaptations of their own that allow them to evade our innate defenses. You experience this every time you contract a cold, flu, or stomach virus. When our innate defenses fail, we rely on our adaptive immune system to destroy the pathogens that make us ill. Our adaptive immune systems do more than fight specific pathogens, though. They also remember those pathogens and prevent us from succumbing to them upon another exposure. The B and T lymphocytes are the key to adaptive immunity.

When pathogens invade, they can be present both inside individual cells and cruising around the tissues. Fortunately, natural selection has provided us with tools to deal with both scenarios. B cells produce special chemicals, called antibodies; these are our mobile defenses, able to detect and defeat mobile pathogens. A single B cell, having detected a pathogen, can multiply to produce an army of plasma cells, each of which may secrete up to 100 million antibodies per hour. Because of their specificity, antibodies are useful tools in diagnosing specific diseases and in many kinds of biological research.

Antibodies are great weapons against mobile pathogens. If pathogens have already invaded, though, we need another line of defense. Infected cells have mechanisms allowing them to signal that they’ve been invaded. Cytotoxic T cells recognize those signals and destroy infected body cells. Although this means that we lose some cells, it also means that we reduce the risk of many more cells becoming infected. Cytotoxic T cells are also a major target of research as possible anticancer agents: if they can be programmed to recognize specific markers of cancer cells, they can target and destroy those cells while leaving healthy cells intact. This would be a huge step forward in cancer treatment.

If you had chicken pox as a child, you know you are highly unlikely to contract it again. Your childhood vaccines provide long-term protection against diseases that are potentially fatal to children. People over age 65 accounted for the fewest cases of Spanish influenza; researchers believe that these individuals likely encountered a very similar virus earlier in their lives and had therefore developed partial immunity to the deadly strain. We owe long-term immunity to the secondary immune response, which takes advantage of the memory B and T cells that develop the first time we are exposed to a pathogen.

What should you know?

To fully answer this Driving Question, you should be able to:

1. Identify the components of the lymphatic system and their functions.
2. Define the origin and development of B and T cells.
3. Describe the process that leads to the production of pathogen-specific antibodies.
4. Explain what antibodies are and their role in fighting pathogens.
5. Explain how our bodies develop immunological memory cells that can produce antibodies to an antigen they’ve encountered before.
6. Describe the process that leads to the production of pathogen-specific cytotoxic T cells and how these cells fight pathogens.
7. Explain the relationship between primary and secondary immune responses and the practice of vaccination.

Infographic Focus

The Infographics most pertinent to the Driving Question are 31.3, 31.6, and 31.7 to 31.9.

Identify the components of the lymphatic system and their functions.

21.

Correctly identify the indicated structures from Infographic 31.6 and briefly describe the function of each in the numbered spaces.

1. Bone marrow: where immature white blood cells are produced
2. Thymus: where immature lymphocytes migrate to mature into T cells
3. Lymph nodes: where T and B cells respond to pathogens in the lymph fluid
4. Spleen: where T and B cells respond to pathogens found in the blood
5. Lymphatic vessels: where lymphatic fluid is drained from the tissues and so it can be passed through the lymph nodes on its way back to the tissues

1.5 Driving Question 4:

Why should you care?

You and/or your parents may remember the influenza pandemics of 1968 (the Hong Kong flu); you certainly should remember the H1N1 (swine flu) pandemic that began in 2009. Neither of these events was as severe as the Spanish influenza pandemic of 1918, but they serve as important reminders that influenza pandemics are unavoidable. That’s because influenza viruses change, both gradually via mutation and rapidly via gene swapping. Influenza researchers say that the question is not whether a new pandemic of severe influenza will occur, but when.

What should you know?

To fully answer this Driving Question, you should be able to:

1. Compare and contrast the processes of antigenic drift and antigenic shift.
2. Explain why antigenic shift is more likely to lead to new influenza pandemics than antigenic drift.
3. Explain why public health officials monitor the types of influenza viruses infecting nonhuman animals as part of their surveillance against potentially human pandemic influenza strains.

Infographic Focus

The Infographics most pertinent to the Driving Question are 31.5 and 31.10, and Table 31.1.

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