Immunity and Vaccination Overview

Immunity: Protection from Foreign Threats

• Immunity is the body's ability to resist infection and disease
• Term "immunity" comes from the Latin word "immunis" meaning "exempt"
• Thucydides, an ancient historian, wrote in 430 BC about a plague in Athens where those who had recovered could safely care for the sick, showcasing early understanding of immunity.

Vaccination: Generating Immunity Without Disease

• Vaccination prepares the immune system to fight an infectious agent before it causes disease.
• Widespread vaccine use has significantly reduced disease burden and saved countless lives
• Example: Rabies vaccine, eradication of smallpox, anthrax, and ongoing COVID-19 vaccination efforts.

Herd Immunity: Protecting the Vulnerable

• Herd immunity: Protection of a critical mass of people through vaccination or natural infection, also protects those who cannot be vaccinated
• Measles is a prime example where herd immunity is crucial for reducing the risk of outbreaks.

Components of Immunity: Humoral and Cell-Mediated

• Immunity involves both humoral (antibody-mediated) and cellular components
• Humoral immunity: Antibodies produced by B cells neutralize pathogens
  • Passive immunity: Antibodies obtained from another source (e.g., maternal antibodies)
  • Active immunity: Body produces its own antibodies after exposure to a pathogen
• Cell-mediated immunity: Primarily involves T cells
  • T cells eradicate pathogens, eliminate infected cells, and support immune response

Antigen Recognition: The Foundation of Immunity

• Immune responses rely on recognition molecules, specifically B and T cell receptors.
• These receptors are randomly generated through gene segment rearrangements:
  • B cell receptors bind to specific antigens
  • T cell receptors bind to specific peptides presented by Antigen Presenting Cells (APCs)
• Clonal Selection: When a B or T cell encounters its specific antigen, it is "selected" and activated.
  • Activation leads to proliferation, creating a large number of identical cells (clones) all reactive against the specific antigen.

The Complexity of Pathogens

• Pathogens are classified into four major categories: viruses, bacteria, fungi, and parasites.
• The immune system responds differently to each pathogen, tailoring its response based on the pathogen's structure, location (intra- or extracellular), and other factors.

Pathogen Recognition: The Key to Immune Response

• Pathogen recognition: The crucial interaction between a foreign organism (pathogen) and recognition molecules on host cells.
• Ligands: Include whole pathogens, fragments of pathogens, or products secreted by pathogens
• Pattern Recognition Receptors (PRRs): Encoded in the host's DNA and always expressed.
  • They bind to Pathogen Associated Molecular Patterns (PAMPs) (e.g., peptidoglycan): These are generic molecules common to many different pathogens.
  • Pathogens can evolve to evade the immune system.
• B and T cell receptors: Randomly generated, bind to specific antigens, not generic PAMPs.

Immune Response: A Complex and Specific Process

• Clonal selection and expansion: Key process in generating diverse immune responses to specific antigens.
• Individual B and T cells have unique antigen specificity due to their receptors.
• When a B or T cell encounters its specific antigen, it is activated, proliferates, and forms a clone of identical cells, all reactive against that specific antigen. This process ensures an effective and targeted immune response.

Explore the fundamental concepts of immunity, vaccination, and herd immunity in this informative quiz. Learn how these factors protect against diseases and the importance of widespread vaccination efforts. Test your knowledge on historical insights and current practices in immunology.