B Cell Imm 2 lec 9

What three signals activate CD4 T cells

1. T cell receptor + MHC interaction 

2. Costimulation

3. Cytokines 

What is the Tfh? Where does it come from and where does it go?

Specialized subset of helper T cells

• Helps B cells make high quality antibodies

Comes from: Follicles in lymph nodes

Goes to: Germinal centers of B cell

What are the 2 main way that B cells are activated to produce antibodies?

1. T Cell-Independent (TI) Activation

2. T Cell-Dependent (TD) Activation

How does T Cell-Independent (TI) Activation work

B cell activates without help from a T cell

How does T Cell-Dependent (TD) Activation work?

B cell requires direct physical interaction and cytokine help from a Tfh

Where and how do Germinal Centres form in lymph nodes?

They form inside B-cell follicles triggered by the interaction of B cells with T cells.

What three cell fates can B cells differentiate into following activation by Tfh cells and clonal expansion?

• Germinal center B cells

• Plasma cells (antibody-secreting)

• Memory B cells (resting)

What are centrocytes

B cells

What are centroblasts

rapidly dividing B cells

What is the dark zone

contains only dividing b cells

What is the light zone

Contains Tfh and APC

What is the timeline of the germinal centre

7-12 days

• take a couple weeks to resolve

If you receive a covid vaccine, why does it not impact immediately?

Germinal centres take about 2 weeks to fully develop

• why we don't see optimal antibody production until roughly 2 weeks post-vaccination

what two major antibody modification processes occur exclusively within germinal centers?

• Somatic hypermutation (refining antibody affinity).

• Class switching (altering antibody isotype).

what parts of the antibody are altered in Somatic Hypermutation vs Class Switch Recombination?

• Somatic Hypermutation: Alters the heavy-chain and light-chain V (variable) regions via mutations.

• Class Switch Recombination: Replaces the heavy-chain C (constant) regions with those of another class. This creates a different antibody subclass

What is the first antibody that b cells produce?

• IgM

What is the primary purpose of somatic hypermutation in germinal center B cells?

To increase the affinity of the B-cell receptor for its antigen while maintaining the same specificity

What happens to variable and constant region during Somatic hypermutation?

Nucleotides are mutated exclusively within the Variable (V) region genes (pink), while the Constant (C) region genes (blue) remain unmutated.

• This increases affinity BCR

What specific part of the antibody gene is replaced during Class Switch Recombination, and what is the key rule regarding this process?

• Replaced: Heavy-chain constant-region gene segment (mew region replaced my another segment)

• Key Rule: It changes the constant region only!

How does an activated B cell switch from making IgM to making IgG by altering its heavy chain (IgH)?

the intervening DNA between the VDJ region and C region is removed as an excision circle

• this joins the unchanged VDJ region directly to the downstream C-region gene segment

what three advantages does the secondary immune response have over the primary immune response?

• Response time (Faster)

• Quantity (Higher magnitude of antibodies produced)

• Quality (Switches from low-affinity IgM to high-affinity IgG)

Which antibody class and affinity level dominate the primary response versus the secondary response?

• Primary Response: Low-affinity IgM.

• Secondary Response: High-affinity IgG.

What are the key defining characteristics of Naïve B cells

They bear surface IgM and do not secrete antibodies.

What three features distinguish Plasmablasts from fully differentiated Plasma cells?

Antibody Secretion: Plasmablasts have begun to secrete antibodies vs plasma cells rapidly secrete large numbers of antibody molecules.

Proliferation: Plasmablasts have not yet lost the capacity to proliferate vs plasma cells can no longer divide.

Surface Expression: Plasmablasts still bear surface BCRs vs plasma cells bear little to no surface immunoglobulin.

What umbrella term refers to both Plasmablasts and Plasma cells?

Antibody-forming cells (AFCs).

How is immunological memory demonstrated during a second infection or immunization compared to the first?

Immune responses are of greater speed, magnitude, and quality.

What two major factors underlie immunological memory

• Frequency of antigen-specific B cells and T cells (clonal selection).

• Differentiation of effector cells into long-lived memory cells.