Lecture 21: Cell-mediated immunity

Question 1

Problems with antisera from animals? What’s used these days?

Answer 1

• Going to run out
• Never just one B cell stimulated and not just one epitope that is recognisable by these cells and so polyclonal antibodies are created
• We now use monoclonal antibodies that are fused B-cells and a myeloma cell (B-cell tumour) to make a hybridoma that produces a single type of antibody.

Question 2

T Cell Clonal Activation?

Answer 2

Question 3

Killing methods of Cytotoxic T cells?

Answer 3

• Release of Perforin and enzymes for polymerisation
• Release of hydrolytic enzymes (granules) to enter in the holes made by (1)
• Release of cytokines (TNF-α, TNF-β and IFN-γ) that induce apoptosis

Question 4

Lymphocyte ontogeny?

Answer 4

Essentially they all come from the same source = Bone marrow

Some are matured in the Bone marrow = B Cells and others in the Thymus = T cells

Both B and T cells once matured enter the 2ndary Lymphoid organs

Question 5

B cell ontogeny?

Answer 5

Begins with uncommitted stem cells

Pre-B cells are formed when the genes for the heavy chains are re-organised to form cytoplasmic μ chains.

Upon re-arranging the genes for the light chains - they form Immature B cells as surface IgM molecules form

Mature B cells are formed as Igm and IgD are present on the surface

Question 6

Immunoglobulin genes formation? Importance?

Answer 6

These genes are formed by the transcription, translation and splicing of constant/conserved sections as well as random selection. This occurs for both the heavy and light chain providing a constant and a variable region. Cells become committed to to one VH and VL

• Large variability within the variable region. Not always perfect splicing and so this introduces large amounts more variability
• In both cases it is a one-way process that commits the B cell to a certain lineage
• Centeral tolerance can happen within the bone marrow by testing these new cells against bone marrow cells. (Cells with high affinity against our cells are deleted)

Question 7

Class switching in a response to a foreign antigen.

Answer 7

Initially IgM is created as Mu is the first within the chain of constant regions. By chopping out interveening sequences they can switch to say IgG but maintain the same variable region and so have the same antigen specificity.

Question 8

How does the thymus vary with age?

Answer 8

As we get older the thymus involutes - it shrinks and becomes a much smaller organ as the number of thymocytes is heavily.

This means that we are not able to produce as many T cells later in life and we rely more on those formed already.

Question 9

TCRαβ Genes variation?

Answer 9

Random arrangement of V and J in the α chains and

Random arrangement of V D and J in the β chains gives us a sequence that will code for the variable region of the α and β chains now making the T cell comitted to a particular receptor structure.

• Once again a one-way processes taking us to a very large number of possibilities of TCR structures.
• This is like B cells indepented in the absence of antigens so can be anti-self

Question 10

Thymus structure?

Answer 10

Question 11

T cell ontogeny? CD4 v CD8?

Answer 11

after variation and committment to a αB TCR then..

We have a positive selection mechanism where the immature T cells test its T cell receptor and CD4/CD8 against HLA molecules within the thymus (positively selecting for some self recognition)

Then there is a Negative selection against anti-self HLA + self peptide (if they dont bind then they will hopefully bind to HLA + non-self peptide)

Finally the survivors express CD3 molecule associated with the cell (transduction signal) and get exported to the secondary lymphoid organs.

(NB: there are still some more peripheral sensitisation techniques as not all self antigens are present in the thymus)