Lecture 33 Flashcards
What type of antibody-producing cells dominate the primary B cell response?
Most IgM-producing cells (some IgD) come from the primary focus.
Where do some B cells go during the primary response to improve their antibody characteristics?
To the germinal center, where they undergo somatic hypermutation and class switching late in the response.
Do memory B cells produce IgM in the secondary response?
Yes, some memory B cells still make IgM.
What is the most common antibody isotype produced by memory B cells during the secondary response?
IgG (some also produce IgA and IgE).
What process allows antibodies to increase in affinity during repeated immunization?
Somatic hypermutation and affinity maturation.
Can memory B cells re-enter the germinal center?
Yes, they can re-enter to undergo further affinity maturation.
What type of surface immunoglobulin isotype do memory B cells express?
Class-switched isotypes, such as IgG.
What molecules are expressed at higher levels on memory B cells compared to naïve B cells?
MHC class II, CD40, and receptors for survival and proliferation.
Why do memory B cells present antigen more efficiently than naïve B cells?
Because they express higher levels of MHC II and CD40, helping them interact more effectively with TFH cells.
Where do memory B cells circulate and reside after activation?
They circulate through the blood and reside in the spleen and lymph nodes.
What happens to most effector T cells after a pathogen is cleared?
At least 90% die by apoptosis, leaving behind antigen-specific memory T cells.
How are naïve, effector, and memory T cell subsets distinguished in mice?
By their surface markers.
Are memory T cells phenotypically closer to naïve or effector T cells?
Effector T cells.
What makes memory T cells easier to activate than naïve T cells?
They require less co-stimulation and express unique receptors (e.g., high levels of CD28).
Do memory T cells still need contact with p:MHC for activation?
Yes, but they are more sensitive and respond faster than naïve T cells.
What happens to memory T cells upon reactivation?
They become effector T cells.
Where are central memory T cells (TCM) found and what do they do?
They reside in/travel between secondary lymphoid tissues and are rapidly reactivated upon antigen exposure.
What is the differentiation potential of TCM cells?
They can differentiate into various subsets depending on the cytokine environment.
Where do effector memory T cells (TEM) travel and function?
They move to and between tertiary tissues, contributing to first-line defense and quickly regaining effector function.
What distinguishes tissue-resident memory T cells (TRM)?
They are permanent residents in previously infected tissues and respond quickly upon reinfection.
Where are CD8+ TRM cells commonly found?
In multiple tissues.
What factors influence whether a T cell becomes a memory T cell?
Cytokines (IL-7, IL-15), Notch1, and the strength of antigen interaction.
What is the role of IL-7 in memory T cell development?
It promotes survival by increasing expression of Bcl-2, an anti-apoptotic factor.
What happens to IL-7 receptor alpha (IL-7Rα) during effector T cell differentiation?
It is downregulated but retained or reacquired by cells fated to become memory T cells.
Are memory CD8+ T cells or CD4+ T cells more abundant?
Memory CD8+ T cells.
Do memory CD8+ T cells need help from CD4+ T cells?
Yes, for their longevity.
What does it mean to “immunize” someone?
To make someone or an animal resistant to a particular infectious disease or pathogen.
What are the two ways protective immunity can be achieved?
Active immunization and passive immunization.
What is passive immunity?
Temporary adaptive immunity from transferring immune products (like antibodies) from an immune person to a nonimmune one.
What are two examples of passive immunity?
Monoclonal antibody therapy for SARS-CoV-2 and antibodies in breastmilk passed from mother to newborn.
What is active immunity?
Adaptive immunity induced by natural exposure to a pathogen or by vaccination.
What does passive immunization involve?
The delivery of pre-formed antibodies.
In what situations is passive immunization especially useful?
- In individuals with immune deficiencies
- For exposure to life-threatening toxins or venoms
- For exposure to fast-acting pathogens that outpace natural immune response
Does passive immunization activate the host’s own immune system?
No, it does not activate the natural immune response.
Does passive immunization generate memory responses?
No, it does not generate immune memory, so protection is not long-lasting.
What is ZMapp therapy and what is it used for?
A passive immunization using 3 monoclonal antibodies, used against the Ebola virus.
What can prevent the activation of naïve B cells in a nonimmunized animal?
Passive transfer of antibodies.
How does passive antibody transfer affect early childhood vaccinations?
Maternal antibodies acquired via placenta or breastfeeding can block activation of the infant’s naïve B cells.
What is “original antigenic sin”?
The phenomenon where, after an effective immune response, memory cells are reused instead of activating new naïve cells that could target different epitopes.
What is the goal of active immunization?
To induce immunity and immune memory.
How can active immunization be acquired?
Through natural exposure (e.g., chickenpox parties) or artificial exposure (e.g., vaccination).
What is a vaccine?
A deliberate exposure to a non-dangerous form or component of a pathogen to induce a specific immune response with memory.
What type of immune responses do vaccines aim to elicit?
Both B cell and T cell responses.
What is the role of adjuvants in vaccines?
They enhance the immune response to a vaccine.
Why might adjuvants be needed if an antigen is a weak stimulator?
To promote local inflammation and recruit more immune cells
To slow down antigen release and prolong immune interaction
What are adjuvants?
Chemicals added to vaccines to boost immune responses.
What type of immune response does Alum promote?
TH2 responses.
What is MF59 and how does it work?
An oil-in-water emulsion adjuvant that slows antigen delivery.
What is AS04 and what type of response does it encourage?
Alum + TLR4 agonist; promotes TH1 responses.
What are attenuated vaccines?
Vaccines made from viruses with multiple mutations that prevent productive infection in healthy individuals.
Why are attenuated vaccines not always safe for immunocompromised individuals?
The attenuated virus may still cause disease in people with weakened immune systems.
Why do attenuated vaccines act as their own adjuvants?
They contain PAMPs (pathogen-associated molecular patterns) that naturally trigger immune responses.
What is the social contract of immunization?
Healthy individuals agree to vaccination for personal and societal benefit, despite no guarantee of benefit or safety.
Are vaccines 100% effective or 100% safe?
No, vaccines are neither 100% effective nor 100% safe.
What is herd immunity?
When a large portion of the population is immune, reducing the likelihood that a susceptible person will encounter an infected individual.
