Adaptive T cell immunity

Question 1

Briefly describe the difference between cluster determinant-4 and cluster determinant-8.

Answer 1

CD4- helper cells, orchestrate the immune response

CD8- cytotoxic cells, destroy infected cells

Question 2

Describe the maturation process of t-cells.

Answer 2

T-cell precursors found in bone marrow migrate through blood stream to thymus gland for maturation.

Thymus gland well adapted for this as they select for useful cells and destroys self-attacking cells.

Question 3

Describe the structure of a t-cell receptor.

Answer 3

Two chains held together in transmembrane regions by disulphide bonds.

Each chain contains a variable region (binds to antigen);
a constant region (t-lymphocyte interaction region) and a cytoplasmic tail which protrudes from membrane into cytoplasm.

Alongside the extracellular portion of the receptor are carbohydrate molecules.

Question 4

Describe the Class 1 pathway.

How does it differ in non-virally infected cells?

Answer 4

Virally infected cells produce viral proteins
A sample of these proteins passes through proteasome and is degraded by digestive enzymes within it.
Viral peptides are transported baby TAP back into ER and passes through Golgi apparatus
Loaded onto MHC1 molecule that holds viral antigen in place extracellular for recognition.
Specific CD8+ T-cell recognises foreign peptide and kills cell.

The MHC1 holds normal host protein which shouldn’t trigger CD8+ T-cells to bind.

Question 5

Describe the Class 2 pathway.

Answer 5

A sample of pathogen is taken extracellularly by endocytosis/phagocytosis.

It is digested within a phagolysosome and the antigen degraded into peptides which are loaded onto MHC2.
Alternatively, B cells internalise and degrade peptide fragments and then load onto MHC2.

Presented on cell surface and CD4+ T cell recognises peptide-MHC3 complex

Question 6

Describe two ways in which CD4 cells “help” the immune response.

Answer 6

1. B cell maturation by activating cytokines and juxtacrine signalling
2. helps macrophages kill organisms by fusing to form giant multi-nucleated cells in order to contain infection (granuloma)

Question 7

Compare the difference between T-cells and B-cells I terms of:

1. Maturation
2. Recognition
3. Receptors
4. Classification

Answer 7

1. B cells mature in bone marrow, T cells mature in thymus gland
2. B cells recognise intact antigen directly from pathogen. T cell recognise peptides on antigen presenting cells e.g. macrophages and dendritic cells.
3. B cells have receptors(antibodies) on cell surface and freely moving in bloodstream. All T cell receptors are attached to cell surface.

B cells mutate their receptors during affinity maturation. T cells don’t mutate their receptors (more stable) however they are made by random somatic recombination between T cell receptors gene segments.

4. B cells subsets show no major differences. T cells divided into CD4 and CD8 based on surface markers.