9.3 Immunological memory and vaccination
3 min read•august 7, 2024
Immunological memory is our body's superhero power against repeat invaders. When we first meet a pathogen, our immune system creates a special team of memory cells that stick around, ready to fight faster and harder next time.
Vaccines are like training camps for our immune system. They introduce harmless versions of pathogens, allowing our body to create memory cells without getting sick. This clever trick protects us and our communities from dangerous diseases.
Immunological Memory
Primary and Secondary Immune Responses
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- Primary immune response occurs upon first exposure to an antigen
- Involves activation and differentiation of naive B and T cells into effector cells
- Effector cells eliminate the pathogen but the response is relatively slow (takes several days to weeks)
- Secondary immune response occurs upon subsequent exposures to the same antigen
- Faster and stronger than the primary response due to the presence of memory cells
- Antibody levels rise more rapidly and reach higher levels compared to the primary response
- Antibodies produced during the secondary response have higher affinity for the antigen (more effective at neutralizing the pathogen)
Memory Cells
- Subset of B and T cells that persist long-term after an infection has been cleared
- Formed during the primary immune response and can survive for years or even decades
- rapidly differentiate into plasma cells upon re-exposure to the antigen, producing high levels of antibodies
- (both CD4+ and CD8+) mount a faster and more robust response upon re-encounter with the antigen
- Presence of memory cells enables the immune system to respond more quickly and effectively to previously encountered pathogens (provides long-lasting immunity)
Vaccination Strategies
Types of Vaccines
- Vaccines are biological preparations that stimulate the immune system to develop adaptive immunity against specific pathogens
- Attenuated vaccines contain live pathogens that have been weakened (through cultivation in suboptimal conditions or genetic modification)
- Elicit strong and long-lasting immune responses because they closely mimic natural infection
- Examples include measles, mumps, rubella (MMR), and varicella (chickenpox) vaccines
- contain killed pathogens that have been treated with heat or chemicals
- Safer than attenuated vaccines but may require multiple doses to induce sufficient immunity
- Examples include polio (IPV), hepatitis A, and rabies vaccines
- contain only specific components of the pathogen (such as proteins or polysaccharides)
- Highly purified and less likely to cause adverse reactions compared to whole-pathogen vaccines
- Examples include hepatitis B, human papillomavirus (HPV), and pneumococcal vaccines
Vaccine Adjuvants
- Substances added to vaccines to enhance the immune response
- Help to increase the immunogenicity of weak antigens or reduce the amount of antigen needed per dose
- Common adjuvants include aluminum salts (alum), oil-in-water emulsions (MF59, AS03), and toll-like receptor (TLR) agonists
- Adjuvants work by creating an inflammatory environment at the injection site, attracting immune cells and promoting their activation
Population Immunity
Herd Immunity
- Indirect protection from an infectious disease that occurs when a large percentage of the population becomes immune
- Reduces the likelihood of an outbreak because there are fewer susceptible individuals for the pathogen to infect
- Protects vulnerable individuals who cannot be vaccinated (infants, immunocompromised, elderly) by decreasing the overall prevalence of the disease
- varies depending on the infectiousness of the pathogen (typically ranges from 70-95% of the population)
- Can be achieved through widespread vaccination programs or natural infection (although the latter is less desirable due to potential complications)
Key Terms to Review (20)
Affinity maturation: Affinity maturation is the process by which B cells undergo a series of mutations and selection events to increase the binding affinity of antibodies for their specific antigens. This mechanism enhances the effectiveness of the immune response, particularly during the humoral immune response, as it allows the production of high-affinity antibodies that can effectively neutralize pathogens. Additionally, affinity maturation plays a crucial role in establishing immunological memory, ensuring a quicker and stronger response upon subsequent encounters with the same pathogen.
Antigen presentation: Antigen presentation is the process by which protein fragments from pathogens are displayed on the surface of antigen-presenting cells (APCs) for recognition by T cells. This crucial step bridges the innate and adaptive immune responses, as it activates T cells, leading to a tailored immune response against specific antigens, and plays a significant role in establishing immunological memory.
Cell-mediated immunity: Cell-mediated immunity is a crucial component of the adaptive immune response that relies on the activation of T cells to combat intracellular pathogens and cancer cells. This form of immunity is distinct from humoral immunity, as it focuses on direct cell-to-cell interactions rather than the production of antibodies. Through the actions of various T cell subsets, such as cytotoxic T cells and helper T cells, cell-mediated immunity plays a vital role in protecting the body from infections and maintaining immunological memory.
Clonal Expansion: Clonal expansion is the process by which specific lymphocytes, such as T cells and B cells, proliferate in response to an antigen, resulting in a large population of identical cells that can effectively respond to that antigen. This mechanism is crucial for developing immunological memory, which enhances the body's ability to recognize and fight off pathogens more effectively upon subsequent exposures.
Cytokines: Cytokines are small signaling proteins secreted by cells that play a crucial role in cell communication within the immune system. They help regulate immune responses by facilitating communication between immune cells, influencing cell growth, differentiation, and activity during both innate and adaptive responses. Cytokines can act in an autocrine, paracrine, or endocrine manner, impacting various aspects of inflammation and immunity.
Edward Jenner: Edward Jenner was an English physician and scientist who is best known for developing the first successful smallpox vaccine in 1796. His pioneering work laid the foundation for immunology and vaccination, demonstrating the concept of immunological memory, where exposure to a pathogen prepares the immune system for future encounters.
Herd immunity threshold: The herd immunity threshold is the minimum percentage of a population that needs to be immune to a specific infectious disease to effectively prevent its spread within that community. When this threshold is achieved, the risk of infection for individuals who are not immune decreases significantly, because there are fewer potential hosts for the pathogen. This concept is crucial for understanding the effectiveness of vaccination programs and how they contribute to the overall health of a population.
Humoral immunity: Humoral immunity is a component of the adaptive immune response that involves the production of antibodies by B cells to neutralize pathogens and their toxins. This type of immunity is crucial for fighting off extracellular pathogens, such as bacteria and viruses, and is distinct from cellular immunity, which focuses on the actions of T cells. Humoral immunity also plays a role in immunological memory, allowing the immune system to respond more effectively upon re-exposure to previously encountered pathogens.
Immune priming: Immune priming refers to the process by which the immune system is exposed to a pathogen or vaccine, leading to an enhanced response upon subsequent encounters with that pathogen. This phenomenon is crucial for developing immunological memory, which enables the immune system to respond more effectively and rapidly in future infections or exposures. It plays a significant role in vaccination strategies, as vaccines aim to prime the immune system, allowing for long-lasting protection against specific diseases.
Immune tolerance: Immune tolerance is a state in which the immune system does not mount an attack against specific antigens, including self-antigens, preventing autoimmune diseases and allowing for the coexistence of foreign tissues or substances. This mechanism is crucial for maintaining homeostasis and preventing excessive immune responses, especially in the context of organ transplants and vaccinations.
Immunoglobulins: Immunoglobulins, also known as antibodies, are specialized glycoproteins produced by B cells that play a critical role in the immune response. They bind to specific antigens, marking them for destruction and neutralizing pathogens such as bacteria and viruses. These proteins are essential for both cellular and humoral immunity, contributing to the body's ability to recognize and remember pathogens for future defense.
Inactivated vaccines: Inactivated vaccines are a type of vaccine created by killing the pathogen that causes a disease, rendering it unable to replicate and cause illness. These vaccines stimulate an immune response without introducing live pathogens into the body, helping the immune system to recognize and combat the actual disease in the future. This approach contributes to immunological memory, allowing the body to remember the inactivated virus or bacteria and mount a swift response upon re-exposure.
Live attenuated vaccines: Live attenuated vaccines are vaccines created from pathogens that have been weakened or modified so that they cannot cause disease in healthy individuals. These vaccines elicit strong immune responses by mimicking natural infections, leading to the development of immunological memory and long-lasting protection against diseases.
Louis Pasteur: Louis Pasteur was a French microbiologist and chemist who is best known for his discoveries in the field of vaccination, microbial fermentation, and pasteurization. His work laid the foundation for the field of immunology and the development of vaccines, significantly influencing how we understand disease prevention and the immune system's ability to remember past infections.
Memory B cells: Memory B cells are specialized immune cells that persist long-term after an initial infection or vaccination, enabling a quicker and more robust antibody response upon subsequent encounters with the same antigen. These cells are crucial for immunological memory, allowing the adaptive immune system to remember past infections and respond more effectively to future threats.
Memory T cells: Memory T cells are a specialized subset of T lymphocytes that persist long-term after an initial infection or vaccination, allowing for a quicker and more effective immune response upon subsequent exposures to the same antigen. They play a crucial role in immunological memory, distinguishing between past and present infections and forming the basis for the body's adaptive immune response.
MRNA vaccines: mRNA vaccines are a type of vaccine that use messenger RNA to instruct cells in the body to produce a protein that triggers an immune response. This approach effectively teaches the immune system to recognize and fight off specific pathogens without using live virus, thus paving the way for immunological memory and effective vaccination strategies.
Pathogen recognition: Pathogen recognition is the process by which the immune system identifies and distinguishes harmful microorganisms, such as bacteria, viruses, and fungi, from the body’s own cells. This ability is crucial for mounting an effective immune response and is central to the development of immunological memory and the efficacy of vaccinations.
Subunit vaccines: Subunit vaccines are a type of vaccine that includes only specific parts of the virus or bacteria, rather than the whole pathogen. This approach helps to trigger an immune response without introducing the entire infectious agent, making them generally safer and reducing the risk of side effects. They are effective in generating immunological memory, enabling the immune system to recognize and respond to future infections by the pathogen.
Vaccine efficacy: Vaccine efficacy is a measure of how well a vaccine performs in preventing disease in a controlled clinical trial, expressed as a percentage reduction in disease incidence among the vaccinated group compared to the unvaccinated group. It reflects the ability of a vaccine to produce an immune response and contribute to the establishment of immunological memory, which is crucial for long-term protection against pathogens.