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.