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Overview of Exam Preparation

  • Exam scheduled for completion today or early tomorrow morning.
  • Review materials to guide study.
  • Reminder: all topics may be tested on the exam.

Adaptive Immune System

Key Components

  • Primary focus on the adaptive immune system.
  • Main cells involved: T cells and B cells.

Functions of T Cells and B Cells

  • B cells contribute to the humoral immune response.
    • Produce antibodies that circulate in blood and fluids.
    • Protective role against pathogens.
  • T cells are part of the cellular immune response.
    • Responsible for direct action against invader cells.
    • Engage in cell-to-cell combat.

Antigens and Immune Response

Definition of Antigens

  • Antigens are substances that trigger an immune response.
    • Can include: viruses, toxins, bacteria, and pollens.

Immune Response Dynamics

  • Immune cells recognize foreign antigens as a threat and mount a response.
  • Antigens activate B cells and T cells, leading to the formation of an adaptive immune response.

B Cells

Mechanism of Action

  • B cells produce antibodies, which:
    • Neutralize pathogens.
    • Tag pathogens for destruction by phagocytes.

Antibody Development

  • Antibodies have a specific shape tailored to neutralize particular antigens.
  • B cells activate in two ways:
    1. Natural infection.
    2. Vaccination (introducing a weakened virus).

Duration of Response

  • Antibodies typically peak in production between 7 to 10 days after exposure to an antigen.
  • Active production occurs in response to illness or prior vaccination.

T Cells

Activation of T Cells

  • T cells require activation from antigen-presenting cells (APCs).
  • Dendritic cells present antigens using MHC (Major Histocompatibility Complex) proteins.

Types of T Cells

  1. Helper T Cells (CD4 cells)
    • Activate B cells and cytotoxic T cells.
    • Release interleukins to stimulate B cell production of antibodies.
  2. Cytotoxic T Cells (CD8 cells)
    • Directly attack infected or cancerous cells.
    • Release perforins and granzymes to destroy target cells.
  3. Regulatory T Cells
    • Help moderate the immune response to prevent overactivity.

Memory T Cells

  • Some T cells become memory cells after an immune response.
  • Memory cells remain in the body, providing faster and stronger responses to subsequent encounters with the same antigen.

Cell-mediated Immunity

Action of Cytotoxic T Cells

  • Recognize infected cells by identifying foreign antigens displayed on MHC proteins.
  • Release perforins that create pores in infected cells.
  • Inject granzymes that induce apoptosis in target cells (self-destruction).

Comparison with Innate Immune Response

  • Natural Killer (NK) Cells (part of innate immunity)
    • Less specific than cytotoxic T cells; respond to a broader range of threats.
    • Identify cells showing reduced MHC due to viral infection or cancer.

Vaccination Principles

Immunological Memory

  • Initial immune response (primary response) is slower, with gradual antibody development and T cell activation.
  • Upon subsequent infections, a faster and more potent immune response (secondary response) occurs due to memory cells.

Challenges in Vaccination

  • Vaccines may be less effective due to rapid changes in viruses (e.g., flu).
    • Vaccination effectiveness can vary (e.g., 10% effective if vaccinating against the wrong strain).

Immune System Functionality

Phases of Immune Response

  1. First Line of Defense: Skin and mucous membranes (physical barriers).
  2. Second Line of Defense: Innate, non-specific immune responses (e.g., inflammation, phagocytosis).
  3. Third Line of Defense: Adaptive immune responses utilizing specific T cells and B cells.

Conclusion

  • Immune response is a collaborative effort of various cells and mechanisms.
  • The balance between innate and adaptive immunity is crucial for effective defense.