L6 - Generation of antibody

Question 1

Plasma cell structure

Answer 1

Large nucleus - transcription of antibodies
Extensive rER - Involved in antibody production
Large Golgi body - large secretion

Question 2

Why are plasma cell nuclei lighter than most other nuclei?

Answer 2

Lots of euchromatin (unwound DNA), making the nucleus lighter

Question 3

B cells: where do they develop, what do they do there, and what cells allow this to happen?

Answer 3

Bone marrow

Re-arrange their immunoglobulin genes

Stromal cells

Question 4

B cell immunoglobin gene rearranging: what is the process and why is it useful?

Answer 4

• B cells express their re-arranged immunoglobulin molecule on the membrane surface as IgM class - if any of these interact very strongly with self-antigens in the bone marrow they are eliminated
• These cells now mature (and additionally begin to express their re-arranged immunoglobulin molecule as an IgD class)
• Allows production of only useful B cells

Question 5

Mature B cells: what do they do and when do they produce antibodies?

Answer 5

Leave bone marrow and move around the body to populate secondary lymphoid organs and re-circulate through the bloodstream

When they encounter their specific antigen in lymph nodes they proliferate and eventually differentiate into plasma cells and long-lived memory B cells

(NB the B cells that leave the bone marrow cannot secrete antibody)

Question 6

B cells: how do they move through lymph nodes?

Answer 6

IF INACTIVE:
* Enter through the bloodstream
* Travel to the cortex
* Exit through efferent lymphatic vessel

IF ACTIVE:
* Enter through the bloodstream
* Travel to the cortex (may be activated here)
* Travel towards the border of the paracortex where T-cells can stimulate activation even more
* Enter medullary cords and then form primary foci and either migrate to the primary follicle (forming a germinal centre) or starts to leave the LN (?????)
* Exit through efferent lymphatic vessel

Question 7

B cell activation: how many signals are required, what is the process, and are there any special cases?

Answer 7

Require 2 signals:
* Signal 1 - recognition by the antigen-specific membrane immunoglobulin (Ig) molecule
* Signal 2 - most often from an interacting CD4+ T cell – this is T cell-dependent stimulation

In some cases – some antigens (e.g bacterial polysaccharides) can deliver strong enough antigens to stimulate B cells without T cells – this is T cell-independent stimulation

In these cases, the antibody is not usually as strong or efficient

Question 8

Marginal zone: what is it, what does it allow to happen, and what is this process required?

Answer 8

The area of lymph nodes where special macrophages collect antigens draining into a lymph node or spleen

These macrophages allow conformational antigens to be recognised by any antigen-specific B cell migrating through the cortex region of the lymph node

More than one B cell receptor (Ig) on the surface of the cell needs to be stimulated – or cross-linked

Question 9

MHC class II molecules: what are they, what do they do, and what are they produced by?

Answer 9

Major histocompatibility complex (MHC) molecules

Present processed antigens

APCs: macrophages, dendritic, and B cells

Question 10

What benefit do B cells have in producing MHC class II molecules?

Answer 10

Allows binding with CD4+ T-cells to further activate B cells

Question 11

What signals are required for B cell differentiation and clonal expansion?

Answer 11

• Co-stimulatory molecules (eg CD154 (CD40L) on the T cell and CD40 on the B cell)
• Cytokines from the T follicular helper cell

Question 12

FDCs: what are they, where are they found, and what do they do?

Answer 12

Follicular dendritic cells

Lymph nodes cortex - primary follicles

Form a network throughout the primary follicle specially designed to hold antigen/antibody complexes on their surfaces in little nodules- iccosomes - holding antigens like this to provide them for stimulated B cells

Question 13

Germinal centres: what parts to them are there?

Answer 13

Mantle zone - surround it

Dark zone - contains centroblasts

Basal dark zone - contains centrocytes (and lots of FDCs)

Apical light zone - contain plasma and memory cells

Question 14

Centroblasts: what are they and what do they make?

Answer 14

Proliferating B cells that down-regulate their Ig membrane receptors and undergo affinity maturation

Centrocytes producing high-affinity antibodies

Question 15

Centroblasts: what is the process behind affinity maturation?

Answer 15

As the centroblasts divide they undergo hypermutation of their H and L chains of their particular Ig molecule – causing random changes in the structure of the hypervariable regions of the antibody molecules

The net result of this is that some cells can now produce antibodies of a slightly higher affinity for the original antigen or a slightly lower affinity

Question 16

Centrocytes: what are they, what do they do, how is affinity maturation done, how effective is it, and what is the final journey of centrocytes?

Answer 16

The name given to centroblasts that have stopped dividing and have begun expressing their surface Ig

They move over the FDCs expressing antigen - if they bind antigen with high enough affinity they will receive a survival signal – if not they die

As the immune response progresses, antigen levels will fall and the centrocytes compete for lesser amounts of antigen – only those of higher affinity will be selected

Very effective and can result in an increase in affinity of 10,000 to 100,000

Surviving centrocytes meet up with activated T-cells again and differentiate into plasma cells that secrete large amounts of high-affinity antibody or turn into memory B cells

Question 17

Class switching: when can it occur, what is it, and what is it controlled by?

Answer 17

During the centroblast/centrocyte stage

The B cell can change its heavy chain constant region from µ (IgM) to γ (IgG) or α (IgA) or ε (IgE) whilst keeping the same heavy chain variable and light chain (the antigen binding parts)

Class switching is controlled by CD4 T helper cells and cytokines - ie without CD40/CD40L only make IgM
* Different cytokines induce the production of different antibody classes e.g. IL-4 induces IgE

Question 18

Cytokine impact on antibody production

Answer 18

Cytokines also influence how much antibody is made

Question 19

What antibody classes does IL-4 affect?

Answer 19

• IgM - inhibits
• IgE - inhibits
• IgA - none
• IgG1 - induced
• IgG2a - inhibit
• IgG2b - none
• IgG3 - induced

Question 20

What antibody classes does IL-5 affect?

Answer 20

• IgM - none
• IgE - none
• IgA - augments production
• IgG1 - none
• IgG2 - none
• IgG2a - none
• IgG2b - none
• IgG3 - none

Question 21

What antibody classes does IFN-γ affect?

Answer 21

• IgM - inhibit
• IgE - inhibit
• IgA - none
• IgG1 - inhibit
• IgG2a - induced
• IgG2b - none
• IgG3 - induced

Question 22

What antibody classes does TGF-β affect?

Answer 22

• IgM - inhibit
• IgE - none
• IgA - induced
• IgG1 - none
• IgG2a - none
• IgG2b - induced
• IgG3 - inhibit

Question 23

What class does IL-21 + IL-4 induce?

Answer 23

IgG1

Question 24

What class does IL-21 induce?

Answer 24

IgG3

Question 25

What class does IL-13 induce?

Answer 25

IgG3

Question 26

What class does IL10, IL21 + TGFb induce?

Answer 26

IgA

Question 27

What class do IL4 and IL13 induce?

Answer 27

IgE

Question 28

What is the typical plasma cell rate of antibody production?

Answer 28

> 2000 Ab per second

Question 29

What converts a B-cell into a memory cell?

Answer 29

The binding of CD154 on the T-cell to CD40 on the B cell

These can then leave the lymph node and go into the circulation