Cell recognition and the immune system Flashcards
Cells
What is immunology ?
The study of the mechanisms by which the body defends itself against attack from foreign material.
What is a pathogen ?
Any biological agent, usually a microorganism, that causes disease or illness to its host
Give some examples of pathogens
Bacteria -> Salmonella, Lyme disease
Viruses -> Flu, HIV
Fungi -> Athletes foot, Ringworm
Protozoans -> Plasmodium (malaria), Amoeba
Parasites -> Fleas, ticks
Worms -> Flatworms
Prions -> Fatal familial insomnia, Mad Cows disease
What are examples of non self material?
- Pathogens
- Cells from other organisms of the same species
- Toxins
- Abnormal body cells
What does the success of the immune system rely on?
- The ability to discriminate between foreign and host material.
- Survival depends on the ability to launch a destructive immune response against non-self cells and the inability to launch a destructive immune response against self cells
What distinctive molecules on the surface of cells identify it as self?
- Protein markers because they have very specific tertiary structures and there is a huge variety of different shapes due to the variety of different combinations of amino acids
What is the name of these protein markers?
- Antigens
What are antigens?
An antigen is any part of an organisms or substance that is recognised as foreign and triggers an immune response and the production of an antibody by lymphocytes
How does the immune system develop in the foetus?
- There are around 10 million different lymphocytes, each capable of recognising a different chemical shape
- Lymphocytes are not produced in response to an infection, but they already exist
- In a foetus, these lymphocytes are constantly colliding with other cells
- Infection in the foetus is rare because it is protected from the outside world by the mother and the placenta
- Lymphocytes will, therefore, collide almost exclusively with the body’s own material
- Some of the lymphocytes will gave receptors that exactly fit the body’s own cells.
- These lymphocytes either die or are supressed
- The only remaining lymphocytes are those that ft foreign material and therefore only respond to foreign material
What are non specific defence mechanisms?
Response is immediate and the same for all pathogens
They can be physical or phagocytosis
What is an example of a physical barrier to entry?
- Skin -> provides physical barrier that most pathogens find difficult to penetrate. Sebdum found on skin with air. Antibacterial fatty acid produced by sebaceous glands. Waterproofs skin and is main constituent in ear wax
- Mucous membrane -> Sticky mucus traps pathogens which can be removed (coughing) or swallowed where it is destroyed by HCl in the stomach
- Cilia -> Cilia waft mucus in respiratory system to back of the throat
- HCl -> provides low pH environment that denatures most pathogen’s enzymes. Protects against pathogens in food and wafted from the lungs
- Tears, saliva, urine -> All have antibacterial qualities. They contain enzymes that hydrolyse proteins in pathogens. Tears contain lysosomes
- Commensal microorganisms -> Good bacteria which help digest food and acquire nutrients like Vitamin B and vitamin K. They also compete with other pathogenic bacteria and prevent them colonising the body.
- Reflexes -> Stop things getting in -> sneezing, yawning and blinking.
What is phagocytosis?
- When phagocytes act to ingest and destroy foreign material.
- They respond in the same way for all pathogens
Describe the process of phagocytes
- The phagocyte is attracted to the pathogen by chemical products of the pathogen. It moves towards the pathogen along a concentration gradient
- The phagocyte has several receptors on its cell-surface membrane that attach to antigens on the surface of the pathogen
- Phagocyte engulfs virus to form a phagosome
- Lysosomes fuse with the phagosome and release lysozymes that will hydrolyse the virus.
- Phagocyte absorbs products from pathogen and displays antigens on its surface and becomes an antigen presenting cell
What are the two types of lymphocytes?
- B lymphocytes ->
Formed from stem cells found in bone marrow of long bones and mature in the bone marrow.
They are associated with the humoral response (antibodies in fluids such as plasma)
They respond to foreign material outside body cells - T lymphocytes
Formed from stem cells in the bone marrow but they mature in the thymus gland.
They are associated with cell mediated immunity and respond to foreign material inside body cells.
How are B cells involved in the humoral response?
- A single B cell has a unique type of receptor molecule on its surface membrane. Each different types of B cell has a different receptor. By chance one of these B cells will have a receptor with the complimentary shape to the antigens on the invading pathogen.
- The B cell with the complimentary receptor to the antigen on the invading pathogen binds to it.
- The antigen moves by endocytosis into the B cell which presents the processed antigens on its surface. This causes T-helper cells to bind to these processed antigens and stimulate the B cells to divide.
- The B cell divides by mitosis to form a clone of B cells cell with the same complimentary receptor to the invading antigen and all capable of producing the antibody that is specific to the foreign antigen.
- The cells of the clone differentiate. The vast majority become plasma cells which release antibodies. A smaller number become memory cells which don’t produce antibodies but remain in the blood for a long time.
How do B cells come about?
The B cells with the complementary receptor to the antigen are not made in response to the pathogen, they were there since birth.
They multiply in response to the presence of the pathogen and release the specific antibody for the specific antigen.
As each clone is only capable of producing one specific antibody, they are called monoclonal antibodies.
What is meant by monoclonal antibodies?
An antibody produced by a single clone of plasma cells
What is a primary immune response?
Immediate defence of the body against infection. it involves the production of antibodies and memory cells.
Why does it take time for the primary immune response to take place?
Antigens and complementary B cell need to collide.
Antigen must be ingested, processed and presented.
Helper T cells need to bind to the B cells
B cells need to divide by mitosis to form a clone.
The clone must differentiate into plasma cells and memory cells.
Only then can plasma cells produce antibodies
What are memory cells and what do they do?
Live longer than plasma cells
They don’t produce antibodies
Circulate in the blood and tissue fluid
When they encounter the same antigen in the future they divide rapidly developing quickly into plasma cells and more memory cells.
Why is the secondary immune response different to the primary immune response?
The secondary immune response produces more antibodies faster than in the primary immune response
This is because when memory cells encounter the same antigen they multiply rapidly to form both memory cells and plasma cells.
These plasma cells are able to produce more antibodies faster
This destroys the pathogen before it has chance to cause symptoms of disease
The new memory cells then circulate in the blood to guard against future attack from the same antigen
We are now immune
