Introduction to Heamatopoiesis II

Question 1

How do we study haemic cells?

Answer 1

The way we do this is by flow cytometry and that’s sometimes referred to as fluorescence activated cell sorting (FACS).

Question 2

Describe flow cytometry

Answer 2

So with flow cytometry, you measure your cells and the fluorescence and then lose the cells.
FACS can actually use the different markers on cells to actually sort cells into collection tubes depending on the markers.
We use a monoclonal antibody which recognises the antigen on the surface of a specific haemic cell to label the cell. The antibody will bind to the antigen and then a second antibody which is fluorescently labelled will bind to the stem structure of the 1st antibody to create a tower of antibodies. The cells are passed through a laser which excites the fluorescent antibody which is then detected by a flow cytometer or another type of spectrophotometric instrument.

Question 3

CD antigens

Answer 3

CD - Cluster of differentiation
A way of naming the different antigens present on the surface of cells. We use specific antibodies to bind to CD antigens to detect types of haemic cells e.g. lymphocytes or T helper Cells (CD4).
Changes in surface antigen expression mark B cell differentiation.

Question 4

What can the immune system be divided into?

Answer 4

Leukocytes are cells that form a major part of the immune system and can be divided into two arms: the innate and adaptive immune system.

Question 5

Innate Immune System

Answer 5

Innate is very fast but non-specific. Adaptive immune system is slow acting but is specific and it can generate immune memory. Within the innate immune system, we have phagocytes (neutrophils, basophils and eosinophils) which can consume foreign particles along with monocytes which can migrate from the blood to tissue to become tissue-resident cells. We also have platelets which are just fragments of cells that play an important role in blood clotting but also an important role in immunity because they can opsonise or create toxic environments for invading pathogens.

Question 6

What cells act between the innate and adaptive immune system?

Answer 6

Natural killer cells are cells between innate and adaptive immune system. So they are innate immune cells, but they are lymphocytes and they are cells which are able to kill virally infected cells as part of their immune surveillance role.

Question 7

Adaptive Immune System

Answer 7

We then have adaptive immune cells e.g. T and B lymphocytes and these are there to provide increased specificity of recognition of pathogens and generation of memory B cells.

Question 8

Neutrophils

Answer 8

Short-lived, motile cells designed to phagocytose bacteria and combat tissue infection

Question 9

Basophils

Answer 9

Only circulating leukocytes that contain histamine, activated by antigen cross linking of FcꜪRI and receptor-bound lgE.

Question 10

Eosinophils

Answer 10

Host defence against nematodes and other parasitic infections.

Question 11

Platelets

Answer 11

Activated by antigen crosslinking of FcyRII

Question 12

What are the two main lymphocytes?

Answer 12

T cells and B cells

Question 13

T cells

Answer 13

The T cells are involved in Cell mediated immunity and can differentiate into T helper cells (CD4+) which are involved in release of cytokines that are involved in directing the immune response and helping other B cells to create antibodies. T cells can also differentiate into T cytotoxic cells (CD8+) and these are directly involved in killing virally infected cells.

Question 14

B cells

Answer 14

The B cells are involved in humoral immunity (production of antibodies and immune memory) through the differentiation into plasma cells.

Question 15

Antigen

Answer 15

An antigen is a molecule, could be a protein or sugar or parts of the bacteria cell wall, that can initiate an immune response.

Question 16

Epitope

Answer 16

A section of amino acids in a 3D structure that is recognised by the lymphocyte receptor is known as the epitope.

Question 17

What do B lymphocyte receptors recognise?

Answer 17

B lymphocyte receptors recognise soluble antigens.

Question 18

What do T cell receptors recognise?

Answer 18

T cells receptors recognise antigens “presented” to the T cell - they need to have the antigen presented to them on a molecule called MHC class one that could be on a surface of a virally infected cell or a dendritic cell (antigen presenting cell).

Question 19

How do T cells and B cells create diversity within the antigen binding region?

Answer 19

Genetic recombination is used which takes place very early in B and T cell development.

Question 20

What do pro T cells and pro B cells do in the thymus to initiate genetic recombination?

Answer 20

So the pro B cells in bone marrow or pro T cells within the thymus will activate expression of the genes that code for the B and T cell receptor respectively and once it does that, it’s committed on its line to differentiate into that specific T-cell or B cell once it starts expressing the receptor gene.

Question 21

What other gene is also expressed along with the receptor genes of pro B and T cells?

Answer 21

This is expressed along another gene called RAG gene (recombinase activating gene) and this acts on segments on DNA that code for the antigen binding region of B and T cells.

Question 22

What segments of DNA are present on the antigen binding region DNA of receptors

Answer 22

Within these antigen binding regions of these receptors, you have segments of DNA that code for either a variable region (V segment), a diversity segment (D segment) or a joining segment (J segment). Many possibilities between the V, D and J segment.

Question 23

What doea the RAG (recombinase activating gene) do?

Answer 23

What happens is the RAG enzyme catalyses genetic recombination, such that the cell will randomly take some V segments, some D segments and some J segments and put them together to form the antigen binding region of the receptor. This will create a receptor that has a pocket that is unique in terms of recognising an epitope on a particular antigen. This is random within each cell that passes through this process.
Estimated that there are more than 10^10 combinations of V, D and J segments. The immune system therefore has the necessary diversity to recognise the wide range of pathogens it comes in to contact with.

Question 24

What happens in the lymphoid system?

Answer 24

Major site of B and T cell interaction with antigen-presenting cells.
Mature naïve B and T cells migrate here to become activated.
Interaction with cognate T helper cells allow adaptive immunity to occur
B cells differentiate:
Undergo SHM ( somatic hypermutation) and class switch to produce high affinity functional antibodies
To long-lived memory cells
To plasma cells
Cd8+ T cells:
Effector (cytotoxic) T cells
Memory T cells

Question 25

Major organs of the lymphoid system

Answer 25

Lymph node and spleen

Question 26

Lymph node

Answer 26

Lymph nodes is where interaction between B and T cells encounter antigen presented cells takes place. These antigen presenting cells pick up and process foreign material, infectious material. Process it into antigens and migrate into the lymph nodes in order to present antigens to lymphocytes.

Question 27

Spleen

Answer 27

The spleen is diverse, divided into two areas, the white and red pulp. The red pulp is responsible for control of red blood cell integrity (recycling of red blood cells and platelets). The white pulp is responsible for the immune function and the organisation is similar to that of the lymph node.

Question 28

How are germinal centres formed?

Answer 28

B cells in lymph nodes are found clustered together as follicular B cells in lymphoid follicles and when activated by an antigen, these lymphoid follicles become germinal centres.

Question 29

B cell Maturation

Answer 29

Germinal centre reaction:
B cells enter lymph node to encounter antigen and help from CD4+ T cells
Affinity maturation occurs to enhance Antibody-antigen interaction.
Generation of immune memory: Memory B cells and plasma cells.

Question 30

Immunoglobulin Molecule

Answer 30

The basic structure:
Heavy and light chains, encoded by different genes
Constant region functions to bind specific receptors (Fc receptors)
Variable region functions to bind to antigen (determined by VDJ recombination)

Question 31

Immunoglobulin Class Switch

Answer 31

Immunoglobulin class switch requires another genetic recombination event. The same event that mediates SHM (Activation Induced Cytidine Deaminase - AID) also mediates class switch from lgM/lgD to: lgG (1, 2a/b, 3), lgA and lgE

Question 32

Types of Immunoglobulin molecules

Answer 32

IgM, IgD, IgG, IgA and IgE

Question 33

Class switch of immunoglobulin molecules

Answer 33

IgM/IgD to: IgG (1, 2a/g, 3), IgA and IgE

Question 34

IgM

Answer 34

Activation of serum complement

Question 35

IgG

Answer 35

Opsonisation/activation of complement/immune cell activation

Question 36

IgA

Answer 36

Innate Immune cell activation

Question 37

IgE

Answer 37

Innate Immune Cell Activation

Question 38

Defence Against Viral Attack

Answer 38

CD8+ T cells engage with infected cells through interaction with MHC class I presentation of viral peptides.
Immune memory is generated with the help of CD4+ T cells
Antigen-presenting cells interact with both CD4+ and CD8+ T cells, CD4+ T cells help with APCs to interact with CD8+ T cells to promote their differentiation to memory T cells.