immune system

Question 1

allergy definition

Answer 1

an inappropriate immune response to a harmless antigen

Question 2

HLA-B

Answer 2

-HLA-B is a gene that provides instructions for making a protein that sits on the surface of cells and helps your immune system determine which proteins it comes in contact with are from your own body or are foreign and potentially dangerous

Question 3

how do allergies work?

Answer 3

• Most of the time, our bodies accept or tolerate the presence of allergens (type 1 immune response - main cell type involved regulatory T cell)
• in some individuals, the body’s immune cells see the allergen as a threat and a pro-inflammatory response occurs (type 2 immune response - main cell type involved T helper type 2 cells)
• These cells stimulate the production of immunoglobulin E (IgE) molecules
• The 1st exposure to an allergen that results in a Type 2 immune response is called allergic sensitisation
• once the body has been sensitised, it maintains a lasting memory of the substance and when it next comes into contact with the allergen, IgE molecules are primed to release inflammatory molecules e.g. histamine, causing the symptoms of allergy

Question 4

types of T cell

Answer 4

• CD4 helper T cells: the directors of immune responses, helping other cells, including B cells, do their job effectively.
• CD8 cytotoxic T cells: trained to be killers, attaching to infected cells and stimulating these cells to die. This death signal to the infected cell leads to apoptosis which curbs the pathogen, limiting its ability to infect neighbouring cells.

Question 5

B cells

Answer 5

• Activated B cells divide repeatedly
• In some cases they generate plasma cells that make soluble versions of their B cell receptors (i.e. antibodies)
• Plasma cells can live for many years, making antibodies that distribute throughout the body -> form an immediate defence against the pathogens that invade us

Question 6

Tc cell activation

Answer 6

• Tc cells have T cell receptors (TCR) on their surface
• TCRs bind to protein fragments (polypeptide antigens) held on the surface of cells by MHC1
• Naive (inactivated) Tc cells circulate move inside lymph nodes (small kidney-shaped organs) where they scan dendritic cells
• Dendritic cells are covered in MHC1 molecules, each holding an antigen generated from a protein that the dendritic cell phagocytosed
• If Tc cells find an MHC1-antigen complex that their TCR recognises, they stick to the dendritic cell
• CD28 on the Tc cell binds to CD80 or CD86 proteins on dendritic cell surfaces
• Signals pass between the dendritic cell and Tc cell -> Tc cell becomes activated and proliferates

Question 7

how do Tc cells kill other cells?

Answer 7

• Infected, stressed or damaged tissues and cells release small proteins called chemokines that attract activated Tc cells out of blood vessels and into tissues
• In the tissue, activated Tc cells survey local MHC1–antigen complexes and bind to any cell displaying a complementary MHC1–polypeptide antigen complex
• Signals are passed through the TCR that instruct the activated Tc cell to deploy its molecular weapons to kill the cell
• Some activated T cells can become ‘memory’ T cells that stay with you your whole life