Cell Recognition and the Immune System Flashcards
Define antigen (PST)
- A protein/glycoprotein
- Found on the surface of a cell/pathogen/toxin
- That triggers an immune response
Define pathogen
A microorganism that causes disease
What do antigens allow the immune system to identify? (TPCC)
- Toxins
- Pathogens and pathogen-infected cells
- Cancer cells (have abnormal antigens in their cell surface)
- Cells from other individuals of the same species (will have foreign antigens unless from generically identical donor)
Role of the innate immune system
Destroys anything that is recognised as foreign - it is non-specific and fast
Role of the adaptive immune system
Targets a specific antigen - it is specific, slower and provides long-term immunity
What is the order of resort for the innate immune system? (BTIFP)
- Barriers
- Thrombocytes
- Inflammation
- Fever
- Phagocytosis
Give examples of barriers and what do they do?
- Skin
- HCl in stomach
- Cilia/mucus in trachea
- They prevent the entry of every microbe
What do thrombocytes do?
Clotting if the barrier (specifically the skin) is broken
Why does inflammation happen?
- If clotting doesn’t stop pathogens from entering
- Increases the concentration of leukocytes in the blood plasma in that area to fight the pathogen
Why does fever happen?
High temperature
To denature the enzymes in the pathogen so it can’t reproduce
What happens if barriers, thrombocytes, inflammation and fever don’t work?
Phagocytosis
What are the different types of phagocytes? There are 6.
- Eosinophil
- Basophil
- Neutrophil
- Monocyte
- Macrophage
- Dendritic cell
Outline the process of phagocytosis (12)
1) Chemical attraction between pathogen and phagocyte occurs (due to chemical secretions of the phagocyte). This is known as chemotaxis
2) Phagocyte moves towards the pathogen down a concentration gradient
3) Receptors on the CSM of the phagocyte bind to chemicals on the CSM of the pathogen
4) Phagocyte engulfs the pathogen, surrounding it using pseudopodia
5) Pathogen gets trapped in a vesicle - a phagosome is formed
6) A lysosome is synthesised by the phagocyte
7) Lysosome fuses with the phagosome, forming a phagolysosome
8) Hydrolytic enzymes (lysozymes) from the lysosome hydrolyse the pathogen
9) The hydrolysed pathogen debris is released by exocytosis
10) If the pathogen is a monocyte/macrophage, the phagocyte presents the pathogen’s antigens on its cell surface membrane and so becomes an APC. However phagocyte will still keep its own antigens (MHCs) on its CSM so that it isn’t identified as foreign
11) T helper cells come near the phagocyte and identify the foreign antigen
12) The adaptive immune response is triggered
Summarise Phagocytosis in key words
Chemotaxis, attach, pseudopodia, engulf, phagosome, lysosome, phagolysosome, hydrolytic enzymes, exocytosis, APC, adaptive immune response
Where do T-lymphocytes differentiate?
Thymus gland
What does the cell-mediated response target? (AVCT)
Cells which have a foreign antigen presented on their CSM. These are:
- APCs
- Virally infected cells
- Cancer cells
- Transplanted cells
What is the cell-mediated response less effective at targeting? (EF)
- Extracellular pathogens eg bacterial cells
- Free antigens eg allergens, toxins
How does the cell-mediated response start?
- An adaptable CD4 receptor from a T helper cell fits exactly onto a foreign antigen presented by an APC
- This causes the T Helper cell to rapidly divide by mitosis and form many genetically identical clones of itself (T-memory cells)
After the T-helper cell divides by mitosis to form T-memory cells, what 4 things happen?
1) T-memory cells circulate in the blood and readily respond to any future infection by the same pathogen
2) Cytotoxic T-cells are activated and release perforins - a protein which makes holes in the CSM of abnormal cells, causing it to become permeable —> lysis —> cell dies as CSM can’t function.
The T-helper cell also releases cytokines. These do 2 things:
3) Send messages to phagocytes to get more of them to destroy the pathogen
4) Stimulates B-lymphocytes to divide so complementary antibodies can be produced - this starts the humoral response
What is the most common cytokine?
Interlukin
Why are B-lymphocytes called so?
Because they differentiate in the bone marrow
Where does the humoral response take place?
- In the body’s humour - the blood and lymph
Where does the cell-mediated response take place?
Within infected cells
What does the humoral response produce?
- Complemetary antibodies
