✅5 - Cell Recognition and the Immune System Flashcards
Each cell has specific molecules on its surface that…
…identify it.
Which molecules can the immune system identify?
- pathogens
- cells from other organisms of the same species
- abnormal body cells
- toxins
What is an antigen?
Any part of an organism or substance that is recognised as non-self by the immune system and which stimulates an immune response.
What are antigens affected by?
- Invading microorganisms
- Cells that have been infected by a virus
- Cancer Cells
- Cells transplanted from another organism
- Allergens such as pollen
Where are antigens found?
On the cell surface membrane as proteins or glycoproteins
What are non-self antigens?
Ones not recognised by the body which cause an immune response.
What is an antibody?
A molecule secreted by lymphocytes in response to stimulation by the appropriate antigen.
What are the characteristics of bacteria?
- Microscopic
- Living cells that can multiply rapidly
- Attack tissues in host and release toxins
- Examples: food poisoning, cholera
What are the characteristics of viruses?
- Ultra microscopic
- Once inside the host, viral DNA replicated itself 1000s of times
- Burst out of host cell into bloodstream, difficult to treat
- Examples: cold, flu, HIV
What do phagocytes do?
Engulf the pathogens
What do lymphocytes do?
Make antibodies which neutralise microbes or make them stick together, destroying them.
What do Neutrophils do?
Neutralise the toxins produced by the microbes.
What are the two types of immunity?
Natural and Artificial
How does natural immunity occur?
- Antibodies passed from mother to child
- Antibodies are made when microbes infect the body
How does Artificial Immunity occur?
- ACTIVE: Vaccine with dead or modified (attenuated) microbes injected causing antibodies to be produced ready for real infection
- PASSIVE: Serum of antibodies are injected directly into a person to fight infection
What is malaria caused by?
Plasmodium
What is phagocytosis?
A process in which pathogens are ingested by a phagocyte (macrophage)
Describe the process of phagocytosis:
- Phagocyte is attracted to the pathogen by chemical products of the pathogen. It moves towards it on a concentration gradient
- The surface receptors on the phagocyte attach to chemicals on the surface of the pathogen
- Invagination occurs and a phagosome forms
- Lysosomes release lysozymes into the phagosome, hydrolyse the bacteria
- The hydrolysis products of the bacterium are absorbed by the phagocyte
Describe the process of lymphocytosis:
- Lymphocyte approaches bacterium
- Antibodies attach to antigens on the bacterium, neutralising them because they can not replicate
What is cell mediated immunity?
Lymphocytes respond to an organisms own cells that have been infected by non self materials from a different species
What is an antigen-antibody complex?
When a complimentary antibody and antigen join
What is an antibody?
A molecule secreted by a B lymphocyte in response to stimulation by the appropriate antigen.
What happens when water rushes to a new wound?
It enters the cells by osmosis and then, because bacteria cells are microscopic they undergo lysis.
Which cells remember antibody production?
Memory B Cells and Helper T Cells
How many polypeptide chains are there in an antibody molecule?
4, joined by disulphides bridges
What are the 4 duplicated regions of an antibody molecule?
Variable and light regions on the heavy chain, and variable and light regions on the light chain.
What does the generic constant region allow and antibody to do?
Attach to phagocytic cells
What does the variable region allow an antibody to do?
It is specific (complimentary) to a particular antigen, which it binds to, depending on the amino acid sequence
What does the hinge region allow the antibody to do?
Flex in order to bind with more than one antigen (accommodation)
What are specific defence mechanisms?
Where the body produces specific antibodies in response to specific antigens associated with specific pathogens.
What are the cells which produce antibodies called?
Plasma cells, derived from lymphocytes.
What is humoral immunity?
So called because it involved antibodies which are soluble in the blood and tissue fluid of the body
What is endocytosis?
The process by which an antigen enters the B cell
What is clonal selection?
When Helper T cells bind to processed antigens and stimulate B cells to divide by mitosis to form cones which produce the same antibody for a specific antigen
Toxins act as…
…antigens
What are plasma cells?
They secrete antibodies into the blood plasma and only survive for a few days but produces antibodies which lead to the destruction of the antigen
What is the primary immune response?
The production of antibodies and memory cells
What are memory cells?
Do not produce antibodies but circulate in blood and tissue fluid. When they encounter the antigen at a later date, the divide rapidly and develop into plasma cells and more memory cells
What are memory cells responsible for?
The secondary immune response
What is the role of B cells in immunity?
The surface antigens of invading pathogen taken up by B cell
B cell processes antigens and presents them
Helper T cells attached to processed antigens on B cell, activating it
B cell activated to divide by mitosis to give clone plasma cells
Cloned plasma cells produce and secrete specific antibody that fits the antigen on pathogen’s surface
Antibody attaches to antigens on pathogen and destroys them
Some B cells develop into memory cells, can respond to future infections by same pathogen by dividing rapidly and developing into plasma cells that produce antibodies
What are antibodies synthesised by?
B Cells
How do antibodies assist the destruction of bacterial cells?
They cause agglutination of the Cells, making it easier for them to be found by phagocytes
They then serve as markers that stimulate phagocytes to engulf the cells to which they are attached
How do cytotoxic T cells kill infected cells?
Produce protein call perforin that makes holes in the cell membrane, allowing other substances in and killing the cell
How does the antibody lead to destruction of the antigen?
They cause agglutination of the cells, making it easier for phagocytes to find them
They serve as markers to stimulate phagocytes to engulf bacterial cells
What are monoclonal antibodies?
A single type of antibody than can be isolated and cloned
What can monoclonal antibodies be used for?
Cancer drugs
Why can monoclonal antibodies be used for cancer drugs?
They are very specific to a particular antigen
How do monoclonal antibodies target cancer cells?
They are produced to be specific to antigens on cancer cells
They are given to a patient and attach themselves to receptors on cancer cells
They attach to the surface and block the chemical signals that stimulate uncontrolled growth
What is an example of a monoclonal antibody?
Herceptin - used for breast cancer
What is indirect monoclonal antibody therapy?
Involves attaching a radioactive or cytotoxic drug to a monoclonal antibody, to kill the cells
What are the benefits of indirect monoclonal antibody therapy?
Can be used in smaller doses
Cheaper
Reduced side effects
What are monoclonal antibodies used to diagnose?
Influenza, hepatitis and chlamydia
How are monoclonal antibodies used for pregnancy testing?
If human chorionic gonadotrophin (hCG) is present in a woman’s urine, it binds to the antibodies and the complex moves along the strip to be trapped by another antibody and create a coloured line.
What are the issues with monoclonal antibodies?
Production involves the use of mice, and they must have caner induced deliberately
Some deaths have resulted from use of monoclonal antibodies
Testing for the safety of new drugs present dangers
What is passive immunity?
Produced by the introduction of antibodies into individuals from an outside source, no direct contact with pathogen or antigen
What is active immunity?
Produced by stimulating the production of antibodies by the individual’s own immune system. Direct contact with pathogen is necessary
What is natural active immunity?
Results from an individual becoming infected with a disease under normal circumstances
What is artificial active immunity?
Forms the basis of vaccination and involves inducing an immune response in an individual, without symptoms
What are the features of a successful vaccination programme?
Must be economically available in sufficient quantities to vaccinate most of population
Must be few side effects
Means of producing, storing and transporting vaccine must be available
Must be means of administering the vaccine properly
What is herd immunity?
When a sufficiently large proportion of the population has been vaccinated to make it difficult for a pathogen to spread within that population
Why would a vaccinated not eliminate a disease?
Vaccination fails to induce immunity in certain individuals such as those with weak immune systems
Individuals may develop disease immediately after vaccination, not immune
Pathogens mutate frequently
What is antigenic variability?
When the antigens change suddenly rather than gradually
What are the ethics surrounding vaccines?
Production often involves animals
Vaccines have side effects that can cause long term harm
They need to be tested
The expense of the production of the vaccine
What are the features of a HIV virus?
Attachment protein RNA Reverse transcriptase Capsid Lipid envelope Matrix
How does HIV replicate?
HIV enters bloodstream and circulates body
A protein on HIV binds to CD4, most commonly on helper T cells
The protein fuses with cell membrane, RNA and enzymes enter cell
Reverse transcriptase converts RNA to DNA
New DNA moved into helper T cell’s nucleus where it is put into cell’s DNA
mRNA produced and passed out of nucleus
Protein synthesis mechanisms used to create from mRNA
HIV particles break away from helper T cell
How can HIV cause symptoms of AIDS?
By killing or interfering with the normal functioning of the helper T cells
What symptoms can AIDS cause?
Diarrhoea and weight loss, infections of the lungs, intestines, brain and eyes as well as some cancers and other infections.
What happens if the immune system does not have sufficient helper T cells?
It cannot stimulate B cells to produce antibodies or the cytotoxic T cells that kill infected cells
What does ELISA test stand for?
Enzyme linked immunosorbant assay
What is the ELISA test used for?
Uses antibodies to detect presence of a protein in a sample as well as the quantity
How is the ELISA test carried out?
Apply sample to a slide to which the antigens in the sample will attach
Wash the surface several times to remove unattached antigens
Add the specific antibody and leave the two to bind
Wash surface to remove excess
Add second antibody to bind with the first, has an enzyme attached to it
Add colourless substrate of the enzyme
What result does the ELISA test give?
The enzyme binds with the substrate and a colour develops. The intensity of colour shows quantity of protein
How does penicillin work?
It inhibits enzymes needed for the synthesis of peptide cross linkages in bacterial cell walls, weakens wall and leads to lysis
