Lecure 33

Question 1

Major immune cell communication methods

Answer 1

• Soluble molecules (cytokines or chemokines) binding to receptors on a cell membrane
• Cell surface-bound receptors binding to cell surface-bound ligand
• Antigen (pathogen parts) being presented to cell surface-bound receptors

Question 2

Soluble chemical messengers binding to receptors

Answer 2

• cytokine binds to the cytokine receptors and it goes straight to the nucleus
• chemokine binds to the chemokine receptor, this activate molecules that direct cell movement
  Both of these either increase or decrease gene expression
• PAMP goes into the plasma where it finds TLR and then TLR goes to the nucleus

Question 3

Cell surface-bound receptors binding to cell surface-bound ligands

Answer 3

T cell activation leads to the immune response against specific antigens, while B cell activation results in the production of antibodies to combat pathogens. These interactions are central to the adaptive immune system’s ability to recognize and respond to a wide range of foreign invaders.

Question 4

Antigen being presented to a cell surface-bound receptor

Answer 4

This process describes antigen presentation, a crucial step in the immune response. It starts with dendritic cells capturing antigens. These antigens are then broken down into fragments and presented on the cell surface bound to MHC molecules. When a T cell encounters a dendritic cell displaying the antigen-MHC complex that matches its T cell receptor, it becomes activated, initiating an immune response against the specific antigen.

Question 5

What is ‘antigen’?

Answer 5

• Anything that has the potential to be recognised by the immune system
• Foreign antigen: anything from ‘outside’ (transplants, pathogens, some chemicals)
• Self-antigen: immune system usually tolerant of self-antigen

Question 6

Activated dendritic communication with T cells

Answer 6

Activated dendritic cells:
- Make cytokines that bind to receptors on T cell membranes
- Have cell surface-bound receptors that bind to T cell surface-bound ligand (or vice versa)
• Present antigen to cell surface-bound receptors on T cells

This communication leads to activation of the T cell It is an example of innate and adaptive immune responses interacting

Question 7

Antigen being presented on MHC to the TCR

Answer 7

This process is called antigen presentation. It involves dendritic cells capturing antigens, breaking them down, and presenting fragments of these antigens on their cell surface bound to MHC molecules. When a T cell encounters a dendritic cell presenting the antigen-MHC complex that matches its T cell receptor (TCR), it becomes activated, leading to an immune response against the specific antigen.

Question 8

What are the two types of MHC

Answer 8

• MHC-I presents endogenous (intracellular) antigen. Expressed on all nucleated cells.
- MHC-Il presents exogenous (extracellular) antigen.Expressed only on antigen presenting cells such as dendritic cells.

Question 9

Cytokines and Chemokines

Answer 9

Cytokines are molecules such as interleukins and interferons that control growth and activity of immune cells

Chemokines are molecules that stimulate cell migration

Both are produced by innate and adaptive immune cells as well as cells that influence the immune system (eg epithelial cells)

Question 10

Helper T cells activate B cells

Answer 10

Helper T cells that have been activated by a dendritic cell can then “help” B cells by:
• Making cytokines that bind to receptors on B cell membranes
- Have cell surface-bound receptors that bind to a B cell surface-bound ligand (or vice versa)

This communication leads to activation of the B cell, and helps the B cell to make antibodies

Question 11

Linking innate and adaptive immunity: B cells and complement

Answer 11

Antibody binding to a pathogen can trigger the classical pathway of complement activation
AND … complement fragments that are bound to antigen can also help activate B cells to make antibodies
These are both examples of how innate and adaptive immunity interact with each other

Question 12

Summary: putting it all together

Answer 12

1. Stand on nail, breaking the physical barrier (skin)
2. Pathogens (eg bacteria) enter the body
3. Chemical mediators lead to vasodilation and entry of phagocytic cells to the tissue to “eat and destroy”
4. The complement pathway is triggered
5. Dendritic cells in the skin become activated through recognition of pathogen associated molecular patterns
6. Dendritic cells move to the local lymph node
7. Activated dendritic cells activate T cells via MHC
8. Antigen + T cells and complement activate B cells
9. B cells produce antibody
10. Complement, phagocytosis and antibodies help clear the pathogen