NU551 Unit 2 Study Guide: Immunity, Infection, and Stress Overview

NU551 Unit 2 Study Guide: Immunity, Infection, and Stress Overview

Student Name

Purdue University Globle 

NU551 Advanced Physiology and Pathophysiology Across the Lifespan

Prof. Name

Date

NU551 Unit 2 Study Guide: Immunity, Infection, and Stress Overview

Immunity protects the body through two interconnected systems: innate immunity, which provides immediate, non-specific defense, and adaptive immunity, which develops targeted, long-lasting protection against specific pathogens. When infections occur, the immune system triggers inflammation to eliminate harmful microorganisms. However, prolonged stress can weaken immune function by increasing cortisol levels, making individuals more vulnerable to illness and delaying recovery.

Understanding Innate Immunity

Innate immunity is the body’s first and fastest defense mechanism against invading pathogens. It responds immediately to bacteria, viruses, fungi, and parasites without requiring prior exposure. Although it does not target specific microorganisms, it effectively prevents many infections from becoming established.

Key components of innate immunity include:

• Physical barriers: Skin and mucous membranes that block pathogen entry.

• Chemical barriers: Lysozyme enzymes found in tears and saliva, gastric acid, and antimicrobial secretions that destroy microorganisms.

• Cellular defenses: Neutrophils, macrophages, dendritic cells, and natural killer (NK) cells that identify and eliminate invading pathogens.

This rapid response also initiates inflammation, helping recruit additional immune cells to infected tissues.

Understanding Adaptive Immunity

Adaptive immunity develops more slowly than innate immunity but provides highly specific protection against pathogens. It recognizes unique antigens and creates immune memory, allowing the body to respond more rapidly during future exposures.

The adaptive immune system consists primarily of:

• B lymphocytes (B cells): Produce antibodies that neutralize bacteria, viruses, and toxins.

• T lymphocytes (T cells):

  • CD4+ Helper T cells: Coordinate immune responses by activating other immune cells.

  • CD8+ Cytotoxic T cells: Destroy virus-infected and abnormal cells directly.

• Memory cells: Remain in the body after infection or vaccination, providing long-term immunity against recurring infections.

This immune memory is the biological basis for vaccine effectiveness.

Comparing Innate and Adaptive Immunity

Types of Hypersensitivity Reactions

Hypersensitivity reactions occur when the immune system produces an exaggerated or inappropriate response to harmless substances or the body’s own tissues. These reactions are classified into four major types.

Type I: Immediate Hypersensitivity

Type I hypersensitivity develops within minutes of allergen exposure and is mediated by immunoglobulin E (IgE). Mast cells release histamine and other inflammatory mediators, producing rapid allergic symptoms.

Common examples include:

• Anaphylaxis

• Allergic rhinitis

• Asthma

• Food allergies

Type II: Cytotoxic Hypersensitivity

Type II reactions occur when immunoglobulin G (IgG) or immunoglobulin M (IgM) antibodies attack cells carrying specific antigens, leading to cell destruction.

Examples include:

• Hemolytic anemia

• Transfusion reactions

• Hemolytic disease of the newborn

Type III: Immune Complex Hypersensitivity

In Type III hypersensitivity, antigen-antibody complexes accumulate within tissues and blood vessels, triggering inflammation and tissue damage.

A common example is:

• Systemic lupus erythematosus (SLE)

Type IV: Delayed Hypersensitivity

Type IV hypersensitivity is mediated by T lymphocytes rather than antibodies. Symptoms typically appear 24–72 hours after exposure.

Common examples include:

• Tuberculin (TB) skin test

• Contact dermatitis

• Poison ivy reactions

Infection Mechanisms and the Immune Response

Infections develop when pathogens invade the body, multiply, and overcome host defense mechanisms. Common infectious agents include:

• Bacteria

• Viruses

• Fungi

• Parasites

As pathogens spread, the immune system activates inflammatory pathways to limit infection and promote healing.

Common signs of systemic inflammation include:

• Fever

• Leukocytosis (elevated white blood cell count)

• Increased C-reactive protein (CRP)

• Fatigue

• Localized redness, warmth, swelling, and pain

These inflammatory responses help eliminate pathogens while initiating tissue repair.

How Stress Affects Immunity

Stress significantly influences immune system function through activation of the hypothalamic-pituitary-adrenal (HPA) axis.

The physiological process follows this sequence:

1. Stress activates the hypothalamus.

2. The pituitary gland releases adrenocorticotropic hormone (ACTH).

3. The adrenal glands release cortisol.

4. Cortisol increases blood glucose while suppressing immune cell activity.

Although short-term cortisol release helps the body adapt to acute stress, prolonged elevation can impair immune defenses.

Health Effects of Chronic Stress

Persistent stress contributes to immune dysregulation and increases susceptibility to both infectious and chronic diseases.

Long-term consequences include:

• Reduced immune response

• Delayed wound healing

• Increased infection risk

• Depression and anxiety

• Cardiovascular disease

• Elevated blood glucose

• Chronic inflammation

Managing stress through healthy lifestyle practices can improve immune resilience and overall health.

Key Takeaways

Understanding innate and adaptive immunity helps explain how the body protects itself from infection. Innate immunity provides immediate, non-specific defense, while adaptive immunity generates targeted immune responses and long-term protection through memory cells. Hypersensitivity reactions represent abnormal immune responses that can range from mild allergies to autoimmune diseases. Additionally, chronic stress weakens immune function by increasing cortisol production, making effective stress management an essential component of disease prevention and recovery.

Immune System Overview

• Innate immunity provides rapid, non-specific protection through physical barriers, chemical defenses, and immune cells.

• Adaptive immunity develops targeted immune responses using B cells, T cells, and immune memory.

• Four hypersensitivity reactions (Types I–IV) differ by immune mechanism, timing, and clinical presentation.

• Infection commonly causes inflammation characterized by fever, leukocytosis, and elevated CRP levels.

• Chronic stress activates the HPA axis, increases cortisol production, suppresses immunity, and contributes to chronic disease.

Frequently Asked Questions

What is the difference between innate and adaptive immunity?

Innate immunity is the body’s immediate, non-specific defense against pathogens, whereas adaptive immunity develops a targeted response using B and T lymphocytes and creates long-lasting immune memory.

What are the four types of hypersensitivity reactions?

The four hypersensitivity reactions include Type I (immediate, IgE-mediated), Type II (cytotoxic, IgG/IgM-mediated), Type III (immune complex-mediated), and Type IV (delayed, T-cell-mediated).

Which immune cells produce antibodies?

B lymphocytes (B cells) differentiate into plasma cells that produce antibodies against specific antigens.

What are CD4+ and CD8+ T cells?

CD4+ T cells coordinate immune responses by activating other immune cells, while CD8+ T cells directly destroy infected or abnormal cells.

How does chronic stress weaken immunity?

Chronic stress activates the HPA axis, increasing cortisol production. Persistently elevated cortisol suppresses immune cell function, increases susceptibility to infections, delays wound healing, and contributes to chronic diseases.

References

Abbas, A. K., Lichtman, A. H., & Pillai, S. (2023). Cellular and molecular immunology (10th ed.). Elsevier. https://www.elsevier.com/books/cellular-and-molecular-immunology/abbas/978-0-323-75748-5

Kumar, V., Abbas, A. K., & Aster, J. C. (2024). Robbins & Cotran pathologic basis of disease (11th ed.). Elsevier. https://www.elsevier.com/books/robbins-and-cotran-pathologic-basis-of-disease/kumar/978-0-323-53113-9

McCance, K. L., Huether, S. E., Brashers, V. L., & Rote, N. S. (2023). Pathophysiology: The biologic basis for disease in adults and children (9th ed.). Elsevier. https://www.elsevier.com/books/pathophysiology-the-biologic-basis-for-disease-in-adults-and-children/mccance/978-0-323-78305-7

NU551 Unit 2 Study Guide: Immunity, Infection, and Stress Overview

OpenStax. (2023). Anatomy and Physiology 2e – The immune system. https://openstax.org/books/anatomy-and-physiology-2e/pages/21-introduction

World Health Organization. (2024). Stress. https://www.who.int/news-room/questions-and-answers/item/stress