2C Flashcards
What are Antigens?
Antigens are proteins which generate an immune response when detected by the body. Found on the surface membrane of cells, Antigens that aren’t naturally found in the body are called Foreign Antigens.
What are Pathogens?
They are organisms which cause disease. All pathogens have antigens on their surface, these foreign antigens are identified by the Immune system
Abnormal body cells have…
Cancerous/Pathogen-infected cells have abnormal antigens on their surface, triggering the Immune response
What are Toxins?
They are molecules which are poisons. Some are produced by bacteria, and the immune system responds to the toxins and the pathogens which produced the toxins
Cells from other individuals of the same species and the immune system
When cells are received from other people (Organ transplant/ Blood transfusion) those cells will have some antigens on their surface. If these antigens are different than the antigens of the recipient, an immune response will be triggered - this can lead to the organ being rejected.
What is a Phagocyte? (Macrophage)
A white blood cell which carries out phagocytosis. They’re found in the blood and in tissues. They are the first cells to respond to an immune system trigger
Phagocytosis
Bacteria will attract a Phagocyte/Macrophage by chemoattractants, they then recognise the foreign antigens on a pathogen. The Phagocyte’s cytoplasm moves around the pathogen, engulfing it.
The Pathogen is now contained in a PHAGOCYTIC VACUOLE.
A Lysosome, containing lysozyme’s (Lytic Enzymes), fuses with the phagocytic vacuole, breaking down the pathogen.
The Phagocyte then presents the pathogens antigens on its surface, to activate other immune system cells. The Phagocyte is now a antigen-presenting cell
What are T-Lymphocytes (T-Cells)
It is a white blood cell which has receptor proteins on its surface. When a complementary antigen binds to it, presented by either the Phagocyte/infected cell/B-Cell, it activates the T-Cell to divide by mitosis into either:
Helper-T-Cells, which release chemical signals/bind to receptors on B-Cells to activate them (secrete antibodies) and stimulate Phagocytes, Cytotoxic/Killer T-Cells - which kill abnormal cells by releasing PERFORIN that lyse (make holes in) the membrane of the pathogen. T-Cells also divide into memory cells that rapidly respond if infected again.
Where do the T-Cells mature?
Thymus gland
Where do the B-Cells mature?
In the Bone Marrow
What do B-Cells respond too?
Foreign material outside the body, such as bacteria and viruses
What do T-Cells respond too?
Foreign material inside the body, such as cells altered by viruses, cancer to transplant tissue
What are Antibodies?
Protein molecules, produced by B-Cells (Plasma cells) in response to stimulation by an antigen. They have binding sites specific to a complementary Antigen and when attached, an Antigen-Antibody complex is formed. Their tertiary structure of the binding sites is specific to the antigen. Antibodies have two binding sites
What are B-Lymphocytes? (B-Cells)
They are a type of white blood cell which are covered in antibodies and receptors. Each B-Cell has different shaped antibodies on its membrane, binding to different, specific antigens. When an antigen binds to the antibody, it activates the B-Cell to present the antigen on their surface membrane - becoming an Antigen-Presenting cell (to help activate T-Cells) as well as carry out clonal expansion (rapid mitosis) secreting either Plasma cells (which produce antibodies) or Memory cells, which respond rapidly to another attack by this particular antigen.
What type of immunity are T-Cells?
Cell-meditated Immunity
What type of immunity are B-Cells?
Humoral Immunity
How many years can memory cells live for?
Decades
What can memory cells do?
Divide into plasma cells to produce antibodies if infected by the same pathogen in the future
What is Cell-Meditated Immunity?
Occurs inside infected cells and is mediated by T lymphocytes
What is Humoral Immunity
Humoral immunity is also called antibody-mediated immunity. With assistance from helper T cells, B cells will differentiate into plasma B cells that can produce antibodies against a specific antigen
Antibody production
Plasma cells are identical to the activated B-Cell, secreting antibodies specific to the antigen, called MONOCLONAL ANTIBODIES. They have two binding sites so two pathogens can bind, clumping them together called AGGLUTINATION. Phagocytes then bind to the antibodies and many pathogens at once.
Antibody binding sites are called
Variable regions - with unique tertiary structures. However all antibodies have the same CONSTANT REGIONS
Primary Response
When an antigen enters the body for the first time, activating the body’s immune system. This primary response is slow because there isn’t many B-Cells that can make the specific antibody. Eventually the correct antibody will be secreted, the person will show symptoms of the disease. After being exposed to the antigen, memory cells are produced, allowing a more rapid response and secretion of antibodies if infected again.
Secondary response
If the same pathogen enters the body again, the immune system will produce a quicker, stronger immune response, as the memory cells will trigger clonal expansion of plasma cells faster, producing the specific antibodies for the antigen. The memory T cells will also divide, producing cytotoxic cells to kill any cells carrying the pathogen before any symptoms are shown.
Antigenic Variability
Most of us only develop a disease, such as Chicken pox once, as the pathogen only displays the same antigen, so once the memory cells have been produced, the body can destroy the pathogen before any symptoms are produced.
However, viruses, like the common cold or flu, mutate and change their surface antigens, so the body has no memory cells for this antigen, producing a primary response
Name the two types of Immunity
Passive and Active
What is Active Immunity?
It gets your immune system to make its own antibodies and memory cells. There is two types:
- Natural - becoming immune after catching the disease
- Artificial - Being given a Vaccine
What Is Passive Immunity?
Being given antibodies made from other organisms to fight the pathogen, however the immune system downs produce any antibodies or memory cells. There are two types:
- Natural - When a baby becomes immune for a short amount of time when it receives antibodies from its mother (placenta/breast milk)
- Artificial- Injected from Antibodies from someone else who has been infected with the same pathogen naturally
Active vs Passive Immunity
- Active takes more time to develop protection, whereas Passive is immediate protection
- Active requires exposure to Antigen, Passive does not
- Active makes memory cells, Passive does not
- Active is long-term protection, Passive is short-term protection
What are Vaccinations?
Vaccines contain a pathogens antigens (pathogen is either dead/unable to cause harm) that causes your body to produce memory cells, without showing any symptoms of the disease. This stimulates Active Immunity.
What is Herd Immunity?
Vaccinating many individuals reduces the occurrence of the pathogen so much that those that haven’t been vaccinated are less likely to catch the disease
Features of a successful Vaccination programme
- Suitable vaccine is economically available
- Few side effects
- Means of producing (high technology), Storing (refrigeration - stops antigen protein from denaturing) and transporting the vaccine
- Means of administration (Trained staff to give vaccine)
- Helps whole/most population become immune - Herd immunity
Why do Vaccines not eliminate the disease?
- some people may not respond to the vaccine - vaccine may be inert
- individuals may develop the disease immediately after vaccine before the immune system has had time to prevent symptoms
- Pathogen may have mutated its antigens
- May be so many varieties of the pathogen, not feasible to vaccinate against all
- Certain pathogens can successfully ‘hide’ from the immune system - E.g. inside cells
- Individuals may have objections to vaccines - E.g. religious beliefs, ethical or medical views
Ethical views surrounding the use of vaccines
- All vaccines are tested on animals before humans - some individuals disagree with animal testing. Also some animal-based substances may be used to produce a vaccine which some people may disagree too
- Some people don’t want to risk any side effects, but they are still protected by Herd Immunity, however some think this is unfair.
- Testing vaccines on humans can be risky, they could be exposed to the disease without being fully protected - some may have unprotected sex thinking they are protected against HIV, but can contract it as the vaccine may not have worked.
The use of Monoclonal Antibodies
Monoclonal antibodies are antibodies produced by the same group of genetically identical B-Cells. This can be used in medical diagnosis, E.g. Pregnancy tests, Cancer treatment or transplant surgery
Immunoassay- Pregnancy Test and Monoclonal Antibodies
During pregnancy the placenta produces a hormone called hCG, found in the mothers urine. The pregnancy test contains a monoclonal antibody specific to hCG, which is bound to a coloured bead (blue) When the urine with the hormone hCG travels across the strip of monoclonal antibodies, it binds, and because there’s a high concentration of hCG-antibody complex with coloured beads it changing the colour of the strip
Cancer treatment and Monoclonal Antibodies
Binding of a monoclonal antibody to a receptor antigen presented on a cancer cell surface can halt uncontrolled division or attach to a radioactive or cytotoxic drug to kill only the cancer cells - this reduces side effects that would be experienced if a toxic drug was circulated around the body
Objections to using Monoclonal Antibodies
Monoclonal Antibodies are produced using mice, raising issues with animal testing. They inject the mice with the antigen and kill the mice after a few days, obtaining the lymphocytes from the spleen. They fuse (HYBRIDOMA) the cells with cancer cells to rapidly divide and form a cell culture. They then collect the monoclonal antibodies
What is the ELISA Test
It uses monoclonal antibodies to detect the presence of antigens for diseases, such as AIDS. It is a specific and sensitive test and can also test the quantities of an antigen from the intensity of the colour change.
Antibodies are ‘labelled’ by an enzyme so they can be located, and when an Enzyme-Antibody-Antigen complex is formed, it turns a colourless solution coloured. if there’s a colour change, the pathogen must be present. Other markers, such as fluorescent and Radioactive markers, can also be used to indicate the presence of a complex.
Process of direct ELISA Test
Uses a single antibody that is complementary to the antigen you’re testing for:
- A patient sample are coated to the inside of a well, In a well plate (A plastic tray with lots of circular pits in it) Any Antigens will bind. The well is washed to remove surplus antigen. A detection antibody (with an attached enzyme) that is complementary to the antigen of interest is added. If the antigen of interest is present in the patients sample, it will be immobilised on the inside surface of the well and the detection antibody will bind to it. The well is then washed out to remove any unbound antibodies, and the antibody complex is added (enzyme) it binds to the antibodies. The plate is washed to remove any unbound enzymes and a substrate is added, if the enzyme has bound, it reacts with the substrate to give a colour change - positive result for the pathogen/antigen
What is HIV and AIDS?
HIV is a virus which affects the human immune system. it eventually leads to Acquired Immune Deficiency syndrome (AIDS). AIDS is a condition where the immune system deteriorates and eventually fails, making people infected with AIDS more vulnerable to other infections, like pneumonia.
HIV and Host cells
HIV infects and eventually kills Helper T-Cells, which act as host cells for the virus. Helper T-Cells send chemical signals that activates phagocytes, Cytotoxic T-Cells and B-Cells, so they’re hugely important in the immune system. Without Helper T-Cells, the immune system is unable to defend itself from other pathogens.
Initial infection of HIV
HIV Replicates rapidly and infected people may experience flu-like symptoms. After this period, the replication drops to a lower level. This is known as the LATENCY PERIOD. During this, the person won’t experience any symptoms.
The symptoms of AIDS
People are classed as having AIDS when their Helper T-Cell count drops below a certain level. The length of time between HIV develops to AIDS varies between individuals that have treatment and don’t have treatment, but it is usually 10 years. The length of time people survive with AIDS varies a lot
- Initial symptoms of AIDS include minor infections of mucous membranes and reoccurring respiratory infections
- As AIDS progresses, the T-Cells decreases further, becoming susceptible to more serious infections - severe diarrhoea, bacterial infections and Tuberculosis
- During late stages of AIDS, individuals can experience a range of serious infections such as pneumonia.
HIV Structure
The viral particle has a spherical structure, made with the genetic material of RNA and proteins, including reverse transcriptase - needed for the virus’s replication. It has a Capsid (protein coat) and an extra layer called an evelope, made from the membrane of its previous host cell. The HIV particle also has copies of an attachment protein which helps the HIV attach to the Helper T-Cells.
HIV Replication
- The attachment proteins attaches to the receptor molecule present on the T-Cell’s membrane
- The capsid is released into the cell, where it un-coats and released the genetic material (RNA) into the cells cytoplasm
- Inside the cell, Reverse Transcriptase is used to make a complementary strand of DNA from the viral RNA template
- From this, the double stranded DNA is made and inserted into the human DNA
- Host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA
- The viral proteins are assembled into new viruses, which bud from the cell and go and infect other host cells.
Antibiotics and Viruses
Antibiotics kill bacteria by interfering with their metabolic reactions. They target the bacterial enzymes and ribosomes used in these reactions As viruses don’t have their own enzymes and ribosomes, they use the host cells, antibiotics can’t inhibit them because they would also target other human cells enzymes and ribosomes. Most Antiviral drugs target specific viruses, which use enzymes only in the virus, that exist.
Controlling HIV infection
There is no vaccine or cure for HIV, only antiviral drugs to slow down its progression. The only way to control the virus is to reduce it spreading by safe sex, no sharing needles and if a woman has HIV, not to have children as the virus can be spread to the baby, however not all babies are infected, as anti-viral drugs can reduce the chance of the baby being HIV-Positive
