Germinal Center Reactions Between B and T cells

CASH MONEY

TFH cells more specifically do what when they get an antigen?

Activate B-cells to generate plasmablasts

Are plasma B-cells terminally differentiated?

Yes

Do differentiated plasma cells secrete high levels of antibody?

Yes

Overview of antigen specific B cells in the T zone

1. Chemokines and adhesion receptors triggered by the BCR signal 1 in the node

2. B-cells interact with new T-helper cells to get signal 2+3 to proliferate and make plasma cells (this complex is called a primary focus)

3. Some of the plasma cells form a germinal center off the primary focus

Where can activated B-cells form a germinal center?

Primary follicle in lymph node or spleen

Activated B-cells forming germinal centers overview

1. B-cells encountering antigen form primary foci where proliferating cells migrate to, which forms a secondary follicle with a germinal center

2. Plasma cells migrate to medullary cords or leave via efferent lymphatics

3. Plasma cells migrate to bone marrow

What happens at germinal centers?

Hypermutation of variable regions of Ig genes, all point mutations

Which enzymes mediates hypermutation at the germinal center?

AID, which de-aminates cytosine to uridine

What happens to a germinal center (GC) b cell with low affinity antibodies?

They take him out back and shoot him

What happens to a germinal center (GC) b cell with high affinity antibodies?

It binds the T-cell and gets to mature and proliferate (known as affinity maturation)

What do follicular dendritic cells do?

Leave antigens on their surface on CR1

Reentry into the dark zone is dependent on what?

Reexpression of CXCR4 on centrocytes

B-cell germinal center cycle of cell interactions

1. Bcells mutate their antibody genes in the dark zone of the germinal center

2. B cells w high affinity for antigen can capture and process it for presentation by MHC class II molecules

3. B cells that can present antigens to TFH cells receive survival and mitogenic signals via CD40 and cytokines

What’s the benefit of a booster shot knowing about germinal centers?

Increasing mutations in B cell antibodies over time means higher affinity to the antigen. The booster shots are done later to engage germinal center B cells

What’s the purpose of a germinal center?

To make high affinity antibodies to clear persistent antigens, and then memory cells so they can respond quickly in the future