Immunity — Immunisation

Definitions

Immune System: complex network of cells and proteins that defends the body against infection. They can be classified as:

• Physical barries
• Innate Immunity: Recognize generic pathogenic motifs and directly attack or opsonize and phagocytose
• Acquired immunity: Pathogenic antigens presented to B cells and T cells via APCs such as dendritic cells

Immunization: A process by which a person becomes protected against a disease through vaccination. This term is often used interchangeably with vaccination or inoculation.

Vaccine: A product that stimulates a person’s immune system to produce immunity to a specific disease, protecting the person from that disease.

Immunization:

• Passive
• Active

• Passive Immunization:
  • transfer of preformed antibodies to an unimmunized individual.
  • develop temporary immunity to the particular organism or toxin
  • Once these preformed antibodies have been destroyed, the individual would no longer have immunity to this microorganism or toxin.
  • e.g: Natural: passage of maternal antibodies through the placenta to the fetus
  • e.g: Artificial: administration of pooled human immune gamma globulin and antivenin
• Active immunization:
  • occurs with the exposure of an unimmunized individual to a pathogenic agent
  • Immune system begins the process of developing immunity to this agent
  • produces long-term immunity due to the stimulation of the individual’s immune system.

Stimulation of Immunity by vaccines:

Detection:

• by innate immune system, and/or B-cells
• recognize epitopes on antigens

Primary Response to vaccine administration:

• Innate Immune System activation:
  • Opsonize or bind to agent → aid in engulfment by Antigen-presenting cells (macrophages or monocytes) → insert processed antigen + MHC protein onto its surface
• Complex presented to Adaptive Immune System:
  • Viral: Antigen + MHC I complex → presented to CD8 cell → trigger cell mediated immunity
  • Bacterial or parasitic: Antigen + MHC II protein → presented to CD4 cell → trigger antibody- mediated immunity
• Memory T-cells and B-cells formed → undergo clonal selection following infection, which increases antigen-binding affinity

Subsequent Infection: 2° immune response

• Subsequent exposure to Ag
• memory T cells rapidly proliferate into active helper and cytotoxic T cells specific to that antigen
• memory B cells rapidly produce antibodies to neutralize the pathogen.
• more rapid, prolonged and powerful immune response

Types of vaccines:

• Live attenuated vaccines: produce a strong cellular and antibody responses and typically produce long-term immunity with only one to two doses: MMR, Typhoid
• Inactivated vaccines: Influenza
• Toxoid: Tetanus, diphteria
• Subunit vaccines: Hepatitis B
• Conjugate vaccine: Haemophilus Influenza B vaccine
• Outer membrane vesicle vaccine: B-Meningococcal
• Heterotypic/Heterologous: BCG
• Viral vector: Ebola
• RNA: Pfizer–BioNTech COVID-19 vaccine

JC 2020

Answer by JC