Ch22B_immune_system

Chapter 22B: The Immune System Overview

• Key Concepts

  • Innate vs Adaptive Defense Systems

  • Adaptive Defenses Characteristics

  • Cells involved in Humoral Immunity

  • Cell-Mediated Immunity

The Immune System

• Two Systems Defending Against Pathogens:

  • Innate (Nonspecific) Immunity:

    • Surface Barriers: Physical barriers preventing entry of pathogens.

    • Cells & Chemicals: Natural killer cells, phagocytes, inflammatory responses.

  • Adaptive (Specific) Immunity:

    • Composed of cells specifically adapted to target specific antigens.

Characteristics of Adaptive Immunity

• Five Important Characteristics:

  • Specificity: Targets specific pathogens.

  • Diversity: Can respond to numerous antigens.

  • Memory: Creates lasting immunity against previously encountered antigens.

  • Systemic: Acts throughout the body, not localized.

  • Self-Discriminatory: Differentiates between self and non-self substances.

Activation of Lymphocytes

• Foreign substances (antigens) stimulate maturation and activation of B & T lymphocytes:

  • Recognition & Binding: Lymphocytes bind to antigens to destroy them.

  • Memory Cells: Enable faster immune response upon subsequent encounters with the same antigens.

Understanding Antigens

• Definition of Antigens:

  • Anything provoking an immune response (e.g., bacteria, viruses, toxins).

  • Identified as “non-self” by the immune system

  • Typically large, complex molecules. Pollen grains are highly antigenic to many.

  • Antigenic Determinant (Epitope): Specific portion of an antigen recognized by the immune system.

Cells Involved in Adaptive Defense

• Three Main Cell Types:

  • B Lymphocytes (B Cells): Produce antibodies that react with antigens.

  • T Lymphocytes (T Cells): Directly attack antigens.

  • Antigen-Presenting Cells (APCs): Engulf antigens and present them to T cells for activation.

Branches of Adaptive Immunity

• Cell-Mediated Immunity: T cells attack cellular targets directly.

• Humoral Immunity: B cells differentiate into plasma cells producing antibodies released into body fluids.

Humoral Immunity

• Specific B cells bind to antigens, proliferating into memory and plasma cells.

• Occurs primarily in spleen or lymph nodes.

• Maturation Process: Begins in bone marrow leading to naïve B cells, which migrate to secondary lymphoid tissues.

Immunological Memory

• Primary Immune Response: Initial response upon first exposure to an antigen.

• Secondary Immune Response: Faster and stronger response upon re-exposure.

SARS-CoV-2 and COVID-19 Vaccines

• SARS-CoV-2: Virus causing COVID-19, binds via spike proteins to ACE2 enzymes on host cells.

• Vaccination: Stimulates immune response targeting spike proteins, blocking virus attachment to host cells' ACE2 receptors.

Types of COVID-19 Vaccines

• Current Vaccines Available in the USA:

  • Novavax (Protein subunit)

  • Pfizer-BioNTech & Moderna (RNA vaccines)

  • Johnson & Johnson & AstraZeneca (DNA vaccines, no longer available in the US).

Mechanism of Nucleic Acid Vaccines

• RNA Vaccines:

  • mRNA packed in lipid nanoparticles instructs cells to produce spike proteins, stimulating immune response.

• DNA Vaccines:

  • Hollowed-out viruses deliver DNA that enters nucleus, leading to spike protein production.

Antibody Production and Function

• Antibodies (Immunoglobulins or Ig):

  • Secreted by plasma cells, bind specific antigens.

• Structure: Composed of polypeptide chains (2 heavy, 2 light) with variable and constant regions.

• Function: Inactivate antigens via precipitation, lysis, agglutination, and neutralization (P.L.A.N.).

Adaptive Immune Responses

• Cell-Mediated Immunity:

  • T cells attack infected cells.

  • Helper T Cells (TH): Activate and proliferate B & T cells, amplify innate defenses via cytokine release.

  • Cytotoxic T Cells (TC): Target and kill virus-infected cells and cancer cells.

  • Regulatory T Cells (TReg): Dampens immune response to prevent autoimmunity.

MHC Proteins and Antigen Presentation

• MHC Class I: Displays foreign antigens from within infected cells - found on all except RBCs.

• MHC Class II: Displays antigens from extracellular sources - present only on APCs.

Regulatory T Cell Role

• Role of TReg Cells:

  • Prevent autoimmune diseases by dampening immune responses.

Exam Review Questions

1. The presence of ________ proteins enables immune system differentiation of self vs. non-self. (Answer: b) MHC)

2. The adaptive immune system comprises ______ major cell types. (Answer: d) cell-mediated; humoral)

3. Which is not an antigen-presenting cell? (Answer: a) T lymphocyte)

4. The foundation of long-term immunity relies on ______ cells. (Answer: b) memory)

5. An antibody's mode of action includes immobilization and marking antigens for destruction. (Answer: b)