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In-Depth Notes on Vaccination and Immune Response

Leukocyte Dendritic Cells and Recruitment of Phagocytes

  • Dendritic cells are a type of leukocyte that migrate through the blood.
  • Their primary role is to recruit phagocytes, which are cells that engulf and digest pathogens.
  • This process is crucial for increasing inflammation and can directly result in killing infected cells.

Complement System and Microblysis

  • The complement system creates pores (hole punches) in pathogens, facilitating microblysis.
  • If an infection worsens, infected cells will present antigens through Major Histocompatibility Complex (MHC) class I molecules and secrete cytokines to signal infection.
  • If a cell loses MHC class I, Natural Killer (NK) cells can induce apoptosis (programmed cell death).

Interferons and Cytotoxic T Cells

  • Interferons are chemicals secreted during viral infections, signaling the presence of a virus in the body.
  • This signaling activates cytotoxic T cells, leading to apoptosis of infected cells, and contributes to the formation of memory T cells.

Presentation of Exogenous Antigens

  • Dendritic cells and antigen-presenting cells (APCs) present exogenous antigens (e.g., free-floating) on MHC class II molecules to helper T cells and B cells.
  • This activation enables B cells to produce antibodies targeting the antigen, further activating the complement system.

Vaccine History and the Cowpox Example

  • The concept of vaccination dates back to Edward Jenner, who created a vaccine using cowpox to immunize against smallpox due to their similar antigens.
  • The immune response against cowpox also provides immunity against smallpox.
  • This historical context helps illustrate the similarities in antigens among different viruses.

Ethical Considerations in Vaccination

  • Safety is the foremost consideration when developing vaccines to ensure positive health outcomes without complications.
  • Efficacy examines whether a low dose can elicit a strong immune response and whether the method of inducing immunity is appropriate.
  • Distribution of vaccines must be equitable, ensuring accessibility for all populations.

Herd Immunity Concept

  • Herd immunity occurs when a substantial portion of the population becomes immune to a virus, reducing transmission rates.
  • The concept illustrates that with more immune individuals, the risk to susceptible individuals decreases significantly.

Evolution of Viruses and Impact on Immunization

  • Viruses may evolve from highly infectious and lethal to more contagious but less deadly forms over time.
  • The ultimate goal of vaccines is to establish herd immunity effectively, which can prevent public outbreaks of infectious diseases.

Impact of Vaccination on Disease Prevalence

  • Vaccination has dramatically reduced the occurrence of various diseases; for example, measles cases have decreased significantly since the 1980s.
  • However, there are instances of rising infections in developed regions due to vaccination hesitancy.

Current Issues in Immunization

  • Vaccination still faces challenges such as accessibility, especially in developing nations where healthcare resources are limited.
  • Some pathogens, such as HIV and malaria, remain difficult to vaccinate against; current vaccines are in development.
  • Development of vaccines is costly, requiring significant time and financial investment, usually more than a decade (which was notably accelerated for COVID vaccines).

Vaccine Development Process

  • The vaccine development timeline involves three phases of clinical trials to ensure safety and efficacy:
    • Phase 1: Small group, several months to a year.
    • Phase 2: Larger group, typically another several months to a year.
    • Phase 3: Wider population testing, lasting one to three years.
  • Reporting systems by agencies like the CDC help track vaccine safety post-market.

Immunization Strategies

  • Active immunization involves inducing a sustained immune response by generating memory cells, while passive immunization provides temporary immunity through direct antibody transfer.
  • Vaccines predominantly target viruses, triggering primary immune responses without illness and producing memory cells for future protection.
  • Various types of vaccines include live attenuated, inactivated, or components of pathogens to induce the immune response.