immunity - seneca notes

What are immune systems made up of

Specialised cells that respond specifically to foreign objects and protect an individual from harm

What cells are detected by the immune system cells

• pathogens

• Cells from other organisms

• Abnormal body cells

• Toxins

What are pathogens

• organisms (generally micro-organisms) that cause disease

• E.g bacteria, viruses, fungi, and protists

What are cells from other organisms

• immune cells can detect presence of cells from other organisms of the same species

• E.g organ transplant can induce immune responses

What are abnormal body cells

• immune cells detect the presence of cells in the body that are not functioning as normal

• E.g cancerous cells

What are toxins

• harmful substances produced by pathogens

• Immune cells detect presence of toxins

What are antigens

Immune system responds to pathogens and other foreign bodies due to the presence of antigens

• foreign signals

• Specificity

• Self signals

• Response

Foreign signals in antigens

• antigens are molecules (proteins and glycoproteins) present on the cell surface membrane

• Antigens signal the immune system if the cells are foreign

Specificity in antigens

• every cell has specific antigens

• Antigens bind to the complimentary receptors o the cell surface membrane of the immune cells

• Antigens are foreign, inducing an immune responses

What are self signals in antigens

• not all antigens induce an immune response

• Antigens can also signal if the cells are ‘self’ or they belonging to the host organism

Responses in antigens

Immune system can respond to antigens in a number of ways

• lysosomes break down the foreign cells

• Phagocytosis of the foreign cells

• Production of antibodies that bind to the antigens and inhibit the functioning of the foreign cells

What are the series of steps of the immune response (when foreign object detected by cells)

1. Phagocytosis

2. Activation of T cells

3. Activation of B cells

4. Production of antibodies

Phagocytosis (step one of the immune response)

• pathogens are ingested by specialised cells called phagocytes (White blood cells)

• Pathogens are destroyed inside the phagocytes

Activation of T cells (step 2 of the immune response)

• phagocytes activate T lymphocytes cells (white blood cells)

• Two types of T cells: helper T cells and cytotoxic T cells

• Action of T cells is called cellular response

Activation of B cells (step 3 of the immune response)

• t-cells activate B lymphocyte cells (white blood cell)

• B cells divide into plasma cells

• Action of B cells is called humoral response

• Plasma cells secrete antibodies

• Antibodies are proteins that bind specifically to antigens on the cell surface membrane of pathogens

What are the steps of phagocytosis

1. Detection of antigens → foreign antigens bind to a specific receptors on the cell surface of phagocytes

2. Engulfing the pathogen → the phagocyte moves towards the pathogen. The phagocyte cytoplasm surrounds the pathogen and engulfs the pathogen. The engulfed pathogens is then sealed into a phagosome inside the cytoplasm

3. Digestion of the pathogen → lysosomes fuse with the phagosome and releases proteolytic enzymes into the phagosome so these enzymes can break down the pathogen

4. Presenting the antigens → pathogen antigens transported to phagocyte cell membrane and presented on cell surface. Antigens can activate other cells in the immune response

What are T lymphocytes

• white blood cells involved in cellular immune responses

What are the steps of T lymphocytes

1. Detection of antigens → foreign antigens presented by phagocytes bind to specific receptors on the cells surface of T lymphocyte cells. Binding of the antigens activates T helper cells

2. T helper cells → T helper are a specific type of T cell that activates several cells including phagocytes, T cytotoxic cells and B cells.

3. T cytotoxic cells. T cells are activated by T helper cells. T cells release toxins that bind and kill foreign cells and abnormal cells in the body.

What are B lymphocytes

• white blood cells involved in the humoral immune response

What are the steps of B lymphocytes

1. Activation of B cells → T helper cells activate B cells causing the B cells to divide into identical cells called plasma cells with complimentary receptor to a pathogens antigen called the clonal selection. Once correct B cell is selected, it divides multiple times to produce many identical plasma cells. Plasma cells make antibodies against specific antigens (clonal expansion)

2. Detection of antigens → B cells have specific proteins (antibodies) on cell surface membrane. Each antibody is complimentary to a specific antigen so when they bind an antigen-antibody complex is formed. Binding of antigens to B cells also causes clonal selection

3. Plasma cells → clonal selection leads to clonal expansion which is the production of many plasma cells that have specific antibodies for the antigens present on the body. Antibodies are called mono colonial antibodies, these bind to the antigens of the pathogens

4. Agglutination → clumps the pathogens together, pathogens are then engulfed by phagocytes via phagocytosis. Pathogens are destroyed

What are antibodies

• proteins called immunoglobulins

• Produced by plasma cells during the immune response → Monoclonal antibodies

What is the structure of antibodies

• variable regions

• Constant regions

• Disulphide bridges

• Hinge protein

What are the variable regions on an antibody

• 2 variable regions

• Each antibody has different variable regions

• These regions bind specifically to antigens

• One antibody can bind to 2 antigens. Allows the antigens to clump during agglutination

What are the constant regions on an antibody

• very antibody has the same constant region

What are disulphide bridges on antibodies

• antibodies are made from two heavy chains and two light chains

• Heavy chains are connected to the light chains by disulphide bridges

What is a hinge protein on antibodies

• connects the variable regions to the constant region

What are the uses of monoclonial antibodies

• targeted medication

• Medical diagnosis

How are monoclonal antibodies used in targeted medication

• cancer cells in the body have antigens that signal the cells as abnormal

• Monoclonal antibodies in cancer treatment can be used to bind specifically to antigens on cancer cells

• Cancer treatments can be harmful to many cells, by binding specifically to cancer cells the antibodies allow the treatment onto to be targeted to the cancer cells.

• reduces damage to other cells

How are monoclonal antibodies used in medical diagnosis

• used to indicate the presence of a specific antigen

• Antibodies attached to a dye, fluorescent or radioactive marker

• Complimentary antigen is present, it will bind the antibody and the marker will become visible

• E.g pregnancy tests

What are ELIZA tests

• enzyme-linked immunosorbant assay

• Test for infections or allergies

What are the steps of the ELIZA tests

1. Fixing of the antigens → antigen for the infection is being tested for is immobilised to the bottom of a beaker

2. Addition of the blood → sample of the blood that is being investigated is added to the beaker. If antibodies that are complimentary to the disease-causing antigen are present in the blood, they will bind to the antigens at the bottom of the beaker to form many antigen-antibody complexes

3. Washing of the beaker → the beaker is washed out so that any antibodies that have not bound to antigens are removed

4. Secondary antibodies → secondary antibodies are added to the solution. These are bound to an enzyme. If a secondary antibody binds to the other antibodies from the blood sample, the enzyme will change the colour of a solution

5. Addition of the solution → the solution that reacts with the enzymes on the secondary antibodies is added. If solution changes colour, the secondary antibodies have bound to the antibodies from the blood sample. This indicated the blood sample is infected by the pathogen

What is a primary immune response

• when an individual is infected with a pathogen for the first time a primary immune response takes place

• Slow → takes time for antigens to be detected and the specific plasma cells to be activated. Can take several days for the pathogen to be removed by immune system

• Symptoms → individual is likely to show symptoms of the pathogen. Pathogen has time to cause harm to individual before its removed

• Memory cells → T cells and B cells produce memory cells after an infection. Memory cells remain in the body after the infection has been removed. If the individual is reinfected there is a much quicker response to the antigens

What is the secondary immune response

• when an individual is infected by a pathogen for a second time, a secondary immune response takes place

• Fast → memory cells present so can quickly identify the antigens and produce the correct antibodies

• Stronger → more plasma cells produced more quickly

• Symptoms → unlikely to show symptoms as pathogen is removed before pathogen has time to cause harm. Individual is said to be immune

What are vaccines

Help immune system recognise and destroy pathogens

What are the steps of vaccines

1. Insertion of antigens → vaccines insert the antigens as a weakened or dead pathogen for a specific disease into the individual. Can be inserted by injections or oral insertion (oral vaccinations may be broken down by the stomach

2. Primary immune response → presence of antigens in the body induces the primary response. The antigens are inserted as a weakened or dead pathogen so the vaccine doesn’t give a full scale infection with symptoms

3. Memory cells present→ primary immune cells leads to production of memory cells

4. Immunity → memory cells provide immunity. If the individual is infected by a living pathogen, the memory cells will be ready to induce a fast, strong secondary response

5. Booster vaccinations → given over time to ensure memory cells are still in the body

6. Continuous trail → some vaccinations are continuously being changed because the antigens are evolving at a rapid rate. Pathogens evolve to avoid detection by the immune system, causing problems as it makes vaccines useless. Pathogens with high mutations rate are the most difficult to vaccinate against

What is herd immunity

If enough people in a population are vaccinated against/ have immunity against a disease, the entire population are less likely to be effected

• spread of a pathogen → reduced the chance of someone without immunity coming in contact with the disease

• Population requirements → if disease is highly contagious, 90% of the population must be vaccinated. If less contagious over 8p% of the population must be vaccinated

• Benefit → offers protection to most vunrability people (new born babies and elderly)

What is active immunity

• when immune system has created its own antibodies

• Natural → where antibodies have been created in response to catching a disease

• Artificial → antibodies have been created in response to vaccination of antigens

What is passive immunity

• individual recieves antibodies from an external source

• Not made from individual

• Natural → antibodies transferred to a baby from mothers breast milk

• Artificial → antibodies are transferred to an individual by an injection

What is HIV

• human immunodeficiency virus

• Inhibits immune system

What’s the structure of HIV

• capsid → inside centre of the virus is a protein (capsid) the capsid contains the genetic material and enzymes

• RNA → the genetic material for HIV consists of 2 single stranded RNA, this is found inside the capsid

• Enzymes → enzymes inside the capsid include reverse transcriptase and integrase. Reverse transcriptase and integrase are important in the role of HIV in infection

• Viral envelope → capsid enclosed by a viral envelope. Viral envelope has glycoproteins on its surface. Glycoproteins bind to the cell surface membrane of T helper cells to infect the cells

How does HIV infect the immune system

replicates inside T helper cells

1. Bind to T helper cells → glycoproteins on surface of HIV bind to receptor proteins on cell surface membrane of the T helper cells

2. Release of the capsid → capsid injected into the T helper cells. The RNA and enzymes are released from the capsid

3. Reverse transcriptase → reverse transcriptase is an enzyme that converts the single stranded RNA from the HIV into double stranded DNA. The DNA moves into the nucleus of the T helper cells

4. Integrase → enzyme that inserts the HIV DNA into the T helper cells DNA

5. Expression → the genes in the HIV DNA are expressed in the T helper cells. The HIV proteins are synthesised and the new HIV RNA is made

6. Release of HIV → new HIV viruses are released from the T helper cells. The T helper cells die and the HIV virus can infect more cells

Wh

What is AIDs

Acquired immune deficiency syndrome caused by HIV infection

• cause → when a HIV virus infects a T helper cell and replicated the cells are killed. As HIV spreads and more T helper cells are killed, the immune system is weakened. This results in the individual highly susceptible to infection by other pathogens

• Symptoms → intial symptoms of HIV are similar to the flu. More subceptible to infections with AIDs and may cause them to die from one of these infections

How is HIV treated

• virus so is NOT treated with antibiotics

• Antibiotics specifically target enxymes and ribosomes in bacteria And viruses use host enzymes to replicate so cannot be targeted

• Potential treatment is antiviral drugs to target the reverse transcriptase