BB5MOP Week 16

Define apoptosis.

Tightly regulated process of programmed cell death.

What are the two situations where a cell can die?

1. Where it's given a signal to die.

2. When the cell chooses to die.

What is the term used to describe the 1st situation (signals) in which a cell can die and describe it?

1. Extrinsic pathway

2. Release signals bind to the death receptors on the cell's surface, triggering a cascade of reactions causing it to die.

What is the term used to describe the 2nd situation (choice) in which a cell can die and describe it?

1. Intrinsic pathway

2. Cell recognises its own internal damage such as, damaged DNA and will self-destruct.

What are the cells sending out signals telling a cell to die?

Caspases

What is the control that mediates the release of caspases?

Bcl2 family act as decision markers.

What is the Bcl2 family?

Molecules that regulate cell death and cell survival.

What does apoptosis do to a cell that is dying?

It will shrink it, condensing its DNA and break it up into smaller membrane-bound packages to be engulfed by phagocytosis.

What happens when too much apoptosis occurs?

Leads to neurodegenerative diseases and immunodeficiencies.

What happens when too little apoptosis occurs?

Cancer development

What do T cells do when a pathogen invades the adaptive immune system?

Seeks and destroys infected cells and coordinates the immune response to ensure an organised response.

What are antigen presenting cells (APCs)?

Displays fragments of the pathogens antigen on their cell surface to allow T cells to recognise them and respond.

What are the two classes of MHC molecules involved in APCs?

MHC Class 1 and MHC Class 2

What do MHC molecules give information about?

About where the pathogen is, either extracellular or intracellular.

What type of T cell does MHC Class 1 and MHC Class 2 present?

1. MHC Class 1 presents CD8 T cells.

2. MHC Class 2 presents CD4 T cells.

Describe how MHC Class 1 works.

1. Intracellular pathway, samples proteins throughout the body and presents pathogenic proteins onto cell surfaces.

2. Proteasomes break down proteins into peptides, loaded on endoplasmic reticulum, signal CD8 T cells to clear pathogen.

Where is MHC Class 2 found?

On specialised APCs like dendritic cells, macrophages and B cells.

Describe how MHC Class 2 works.

1. Extracellular pathway, pathogen engulfed into a phagolysosome (phagosome + lysosome).

2. Complex broken down by phagolysosome, displayed onto MHC Class 2, alerting CD4 T cells.

Define cross presentation.

APC is made in MHC Class 2 pathway and then crossed over to MHC Class 1.

What do MHC genes do?

Generate different MHC molecules increasing diversity.

Why is diversity important in MHC molecules?

So the immune system can recognise a wide range of antigens that are being presented.

Why are MHC molecules important for presenting pathogens?

Without MHC molecules, pathogen antigens cannot be recognised by T cell receptors.

Describe the structure of T cell receptors.

Have membrane bound glycoprotein heterodimers, composed of alpha and beta helices.

How do T cells mature?

Grow in the thymus and through gene rearrangement using RAG genes, they are promoted to mature T cells.

How are T cell function and age correlated and give a reason?

1. With age, the effectiveness of T cells decreases.

2. There is not enough space in the thymus to grow and mature more T cells.

What is the difference between young and older people's thymus in relation to T cells?

1. Older people have more immunological T memory cells that take up more thymus space.

2. Compared to younger people who have less so can fight new pathogens better.