Immunobio lectures 9-13 Flashcards
What are the hallmark features of immunological memory?
Longevity, rapid and robust response upon re-exposure, stemness (self-renewal), and enhanced effectiveness compared to the primary immune response.
What is the role of immunological memory in vaccination?
Vaccines aim to induce immunological memory so that upon real infection, the immune system can respond rapidly and effectively, often preventing disease.
What type of antigen typically triggers a T-independent B cell response, and what is the resulting antibody?
Multivalent non-protein antigens (e.g., polysaccharides) trigger a T-independent response, producing mainly low-affinity IgM antibodies.
What type of antigen elicits a T-dependent B cell response and why is T cell help crucial?
Protein antigens elicit T-dependent responses. T cell help (via CD40L and cytokines) is crucial for class switching, affinity maturation, and memory formation.
How do B and T cells interact during a T-dependent response?
B cells present antigen via MHC II to T cells, leading to CD40-CD40L interaction and cytokine signaling, activating B cells for proliferation and differentiation.
What signals are necessary for B cell isotype class switching?
CD40-CD40L interaction and cytokines (e.g., IL-4, IFN-γ) from helper T cells guide the switch to specific antibody isotypes.
What are the functional roles of different antibody isotypes (IgG, IgA, IgE)?
IgG: Neutralization, opsonization, complement activation; IgA: Mucosal immunity; IgE: Defense against parasites, allergy mediator
What two zones exist in the germinal center and what occurs in each?
Dark Zone: B cell proliferation and somatic hypermutation; Light Zone: Affinity selection via follicular dendritic cells (FDCs) and T follicular helper (TFH) cells
What is somatic hypermutation and where does it occur?
It’s the process of introducing point mutations in variable regions of BCR genes to increase antigen affinity. It occurs in the dark zone of the germinal center.
How are high-affinity B cells selected in the germinal center?
B cells compete for antigen on FDCs and T cell help; only those with high-affinity receptors receive survival signals and differentiate further.
What is the difference between long-lived plasma cells and memory B cells?
Plasma Cells: Secrete antibodies for extended periods (often in bone marrow); Memory B Cells: Quiescent, rapid responders upon antigen re-exposure
How do primary and secondary antibody responses differ?
Primary: Slower, lower magnitude, mostly IgM; Secondary: Faster, higher magnitude, mostly high-affinity IgG (or IgA/IgE)
What are the three major subsets of memory CD8+ T cells?
Central Memory (T_CM), Effector Memory (T_EM), Resident Memory (T_RM)
Where are T_CM cells located and what is their main role?
Found in secondary lymphoid organs; they proliferate upon antigen re-exposure and can generate new effector T cells.
What is the functional characteristic of T_EM cells?
They circulate through peripheral tissues and rapidly exert effector functions like cytotoxicity upon encountering antigen.
What distinguishes T_RM cells from other memory T cells?
T_RM cells are non-circulating and permanently reside in tissues (e.g., skin, mucosa), providing rapid local protection at entry points.
What cytokines maintain memory T cells in the absence of antigen?
IL-7 and IL-15 are critical for the long-term maintenance and homeostatic proliferation of memory T cells.
What is the role of follicular dendritic cells (FDCs) in the germinal center?
FDCs present native antigen to B cells in the light zone, allowing selection based on receptor affinity.
What is the role of T follicular helper (TFH) cells in B cell memory formation?
TFH cells provide essential survival and differentiation signals (via CD40L and cytokines) that drive affinity maturation and memory/plasma cell fate.
Why is memory B cell response faster and more robust than naïve B cell response?
Memory B cells have undergone prior selection and affinity maturation, allowing for quicker activation and production of high-affinity, class-switched antibodies.
What are cytokines?
Low-molecular-weight proteins produced by one cell that act on itself or another cell by binding to surface receptors; regulate immune responses.
Are cytokines stored in cells before use?
No. They are rapidly synthesized and released after stimulation; gene transcription is transient and mRNA is unstable to limit synthesis.
How do cytokines exert their effects?
By binding to specific membrane receptors made of one or more transmembrane proteins with extracellular domains for binding and intracellular tails for signaling.
