T cells

Question 1

What do dendritic cells do?

Answer 1

Take up antigen and stimulate T cells in the lymph node or spleen

Question 2

How do dendritic cells use MHC-I and MHC-II to stimulate CD8 ad CD4 cells?

Answer 2

• Dendritic cells use MHC-I to stimulate CD8 T cells.
• Dendritic cells use MHC-II to stimulate CD4 T cells.
  CD4 and CD8 co-receptors assist with the docking of the T cell receptor (TCR) onto MHC-II or MHC-I respectively.

Question 3

How do T cells develop and form effector and memory cells?

Answer 3

• T cells are lymphocytes that arise in the bone marrow and fully develop in the thymus
• T cells express T cell receptor (TCR) with co-receptors (either CD4 or CD8)
• T cells recognise MHC/peptide complexes

Development:
- T cells are produced in bone marrow and are put into the blood to circulate for a short amount of time (immature T cells - thymocytes). They then go into the Thymus, where they undergo rearrangement of the variable parts of their TCR genes. This is done randomly so that each T cell has different receptors (lots of variation), and many of them.
- These Mature (naive) T cells are allowed to leave the Thymus if they do not react to self.
- They then go into the lymphoid organs, blood and tissues.

• Activated T cells are known as effector T cells.
• Memory CD4 or CD8 T cells reside in the body for long periods of time. Memory T cells become effector cells much quicker than naive T cells (bc they are involved in the secondary response if that virus comes back again)

Question 4

How do CD4 helper cells help both CD8 T cells and B cells responses?

Answer 4

CD4 T helper cell:
- Recognises MHC-II/peptide
- Helps CD8 T cell become cytotoxic
- Helps B cells make antibody

Helper T cells do their function by:
- Cytokines (growth factors) produced by CD4 T cells help CD8 T cells become activated.
- Binding to dendritic cells and stimulating them to express co-stimulatory molecules. Can now activate CD8 cell with the help of interleukin 2 secreted by the helper T cell
- Binding to B cell that has encountered its antigen and is displaying MHC-II on its surface. Helper T cell releases interleukins as co-stimulatory signals to complete B cell activation.

CD8 T cell:
- Recognises MHC-I/peptide
- Develops into a cytotoxic T lymphocyte (CTL) aka a cytotoxic T cell once activated
Cytotoxic T Lymphocytes can produce antibody against viruses, making them undergo cell death (apoptosis)

Question 5

What degrades cytoplasmic proteins to peptides?

Answer 5

The proteasome. It is a blender in every cell in the body. Job is to chop up proteins that have extended their life already and to chop up viral proteins. The peptides are then loaded onto the MHC and carried into the body to be displayed.

Question 6

Describe MHC-I antigen processing

Answer 6

• Viral or bacterial infection of a body cell triggers antigen presentation by class I MHC proteins.
• Antigenic proteins are degraded to peptides (in the cytoplasm) by the proteasome
• The ER produces class I MHC proteins to which the abnormal peptides are attached (Peptide loading of MHC-I takes place in the endoplasmic reticulum (ER))
• After export to the Golgi apparatus, the MHC proteins with their bound abnormal peptides are transported to the plasma membrane where they will be displayed.

Question 7

Describe MHC-II antigen processing/loading with peptide

Answer 7

• Antigenic proteins are degraded in acidic phagolysosome
• The ER produces class II MHC proteins and sends them out in a lysosome to bind with the phagolysosome
• Peptide loading of MHC-II takes place in phagolysosome
• It is sent to the plasma membrane where it is presented