Lecture 22: Cell mediated immunity and lymphocyte ontogeny

Question 1

Whats the significance of % serum antibody vs antibody affinity graphs?

Answer 1

• With polyclonal antibodies antibody affinity is a bell shaped curve against % of serum antibody i.e theres a range of affinities and epitopes produced.
• Monoclonal antibodies are created by selecting a single epitope and single affinity (immortalise by fusing ab-forming cells with B cell tumour cells(myeloma))

Question 2

In B-Chronic Lymphocytic Leukemia what is the chemotherapy regime?

Answer 2

If aggressive, RFC chemotherapy

R- Rituximab (Anti-CD20 Mab)
F- Fludarabine (Purine analog, inhibits cell replicaton)
C- Cyclophosphamide (Alkylating agent, anti-mitotic)

Question 3

In non-HLA matched transplants whats the difference between the first and second graft rejection?

Answer 3

First graft - Day 12, mostly T cell mediated destruction

Second graft - Day 5, Mostly antibody mediated

Question 4

Of the millions of T cells, how many epitopes do they recognise?

Answer 4

Each t cell recognizes one epitope with their TcR

CD8 T cell + (APC + Class 1 HLA) requires Thelper cytokines leading to proliferation and differentiation

= Cytotoxic T cells and memory cells

Question 5

What are the three killing mechanisms of CD8 T cells?

Answer 5

1) Perforin + Enzymes for polymerization
2) Hydrolytic enzymes
= Digestive enzyme through pores

3) Cytokines, TNFa, IFNg
= Induced apoptosis

Question 6

What is the origin of lymphocyte precursors?

Answer 6

• Thymus ( T cells)
• Bone marrow (B cells)

and they migrate to secondary lymphoid organs to mature

Question 7

Describe B cell ontogeny?

Answer 7

In the bone marrow:

• Uncommitted stem cells have no antigen specificity
• These develop into Pre-B-cells (Here heavy chains re-arrange genes to commit to antibody type)
• Immature B cells (have surface IgM)(Re-arranges light chains to match heavy)

Leaves bone marrow as mature B cells containing surface IgM and IgD (Express both, committed to one shape)

Question 8

Describe the rearrangement of genes in relation to heavy and light chains:

Answer 8

Light genes: One constant exon, & One variable region is randomly selected and AA removed, added when bound

Heavy genes: Five constant heavy chain exons, Only one VDJ are selected, making hypervariability)

Re-arrangement determines antigen specificity

Question 9

Describe central tolerance in relation to B cells:

Answer 9

• Uncommitted stem cells
• Pre-B-Cell
• Immature B cell -> Gets exposed to self antigen, if strongly reactive then clonal deletion occurs.
• But not all antigens are expressed in thymus so peripheral tolerance is T cell mediated and they dont give cofactors if not appropriate.
• Mature B cell (Surface IgM and IgD)

Question 10

Describe class switching:

Answer 10

Class switching - Removes constant regions by T cell signaling, altering type of immunoglobulin but same specificity.

Question 11

What are the important points of B cell ontogeny and immunoglobulin genes?

Answer 11

• Development in bone marrow
• Multiple VDJ exons recombine = V-region
• Recombination independent of antigen
• Variable region diversity arises from this
• B cells become committed to one V(H) and one V(L)
• Single constant region exons for each class
• Negative selection to remove strong self reactivity
• Class switching retains V-region, changes c-region

Implications
= V,D,J exons important in determining antibody repertoire
= Class switching retains specificity but alters antibody functions

Question 12

The thymus shrinks with age, whats the implication of this?

Answer 12

Fewer new T cells later in life

Question 13

Describe thymus structure:

Answer 13

Insert slide 24

Question 14

Describe T cell ontogeny:

Answer 14

• Uncommitted thymocyte -> TCR gene rearrange
• TCR has both CD4 and CD8, No HLA recognition at all = death (Positive selection)
• HLA recognition is stronger for either CD4 or CD8 and that determines its lineage. (Other CD is down regulated)
• These are exposed to Anti-self HLA + Self peptide, reactivity = negative selection and death.

Those cells that dont react to self peptide survive and are exported to secondary lymphoid organs

Question 15

Whats the important points of T cell ontogeny and T cell receptor genes?

Answer 15

• Development in thymus
• Multiple VDJ exons recombine = V region
• Recombinant independent of antigen
• T cells become comimitted to one Valpha and Vbeta
• Positive seleciton for HLA class one or two recognition (Requires CD4 or CD8)
• Negative selection against strong self-reactivity

Implications

• V, D, J exons important in determining repertoire
• HLA influences T cell receptor repertoire