Cell Recognition And The Immune System Flashcards
Which response is non specific?
- phagocytes
Which response is specific?
- lymphocytes
What is a phagocyte?
- type of white blood cell
Where are phagocytes found?
- blood and tissues
Describe the steps of phagocytosis
- Phagocytes are attracted to dead, damaged or abnormal cells. Given pathogens cause these they are indirectly attracted to pathogens.
- Phagocytes recognise pathogens due to antigens on their surface.
- Pathogens are engulfed to form an phagocytic vesicle
- Lysosomes move towards phagocytic vesicle and fuse with them
- Lysozymes (enzymes) hydrolyse pathogens into monomers.
Define immune system
- System of specialised cells and organs (thymus, bone marrow, lymph nodes) that protect an organism from foreign bodies
What are the two types of immunity?
- innate and adaptive (acquired)
Describe innate immunity
- non specific defence
- no immunological memory
- includes phagocytes, neutrophils and macrophages
Describe adaptive (acquired) immunity
- specific against a particular pathogen
- immunological memory
- includes T lymphocytes (cell mediated) and B lymphocytes (humoral), produce antibodies
What is the first line of defence?
- natural barriers that reduce risk of infection
Give some examples of first line of defence
- Skin and membranes
- Ciliated epithelium (goblet
cells secrete mucus) and trap
microbes in inhaled air - Acid in stomach
- Sweat contains antimicrobial
agents - Blood clots
- Lysozyme present in tears
break down bacterial cells walls (contain murein)
What do molecules have that enables the immune system to identify it?
- proteins/ glycoproteins
What do proteins/glycoproteins enable the immune system to identify?
- Normal body cells
- Pathogens (microorganism that produces an immune response)
- Cells from other organisms of the same species
- Abnormal body cells
- Toxins
Define antigen
- A substance foreign to the body that causes the production of antibodies from the body and causes an immune response
What are examples of foreign bodies (antigens) be?
- A protein on a pathogen
- an infected body cell
- transplanted organ
- cancer cells
Describe antigen variability
- Change of surface protein by microorganisms to evade the immune response
Why are vaccines different each year?
- due to antigen variability (there are many antigenic variants of pathogens)
What does antigenic variants of pathogens lead to?
- affects vaccine design
- affects inability to control some infectious diseases
Define antibody
- A protein with specific binding sites complementary to a specific antigen, synthesised and secreted by plasma cells
Draw the structure of an antibody
- contain antigen binding sites
- Y shape with heavy chain, light chain, Variable regions and constant regions
How many polypeptide chains do antibodies consist of?
- four
What does each tip of the Y of an antibody contain?
- a variable regions that fits one particular complementary antigen which binds the two structures together to form an antigen antibody complex
Which group do antibodies fall into?
- immunoglobulins
What type of protein are antibodies?
- globular glycoproteins
What are the roles of antibodies?
- act as markers to signal phagocytes to engulf bacterial cells
- neutralise to stop pathogen infecting
- cause agglutination of bacterial cells
Where do B lymphocytes mature?
- bone marrow
Which response is B lymphocytes associated with?
- humoral response
Where do T lymphocytes mature?
- Thymus
Which response is T lymphocytes associated with?
- cell mediated immunity
What do T cells only respond to?
- antigens presented on a body cells (recognise antigen presenting cells)
What is the role of an antigen presenting cell?
- present foreign antigens to helper T cells
What are antigen presenting cells?
- cells that display antigens that were on pathogens on their surfaces of the membrane
Describe the steps of cell mediated response (T lymphocytes)
- Pathogens invade body cells or are taken up by phagocytes. Macrophage is a type of phagocyte
- the macrophage places antigens from the pathogen on its cell - surface membrane.
- Receptors on a specific T- helper complementary to these antigens.
- This attachment activates the T-helper cell to undergo clonal selection via mitosis
- Clone of genetically identical memory cells - rapid response to future infections of same pathogen
- Cytokines are released that stimulate B cells to divide and secrete antibodies.
- Cytotoxic T cells are activated that release perforin that make holes in the cell surface membrane.
- T helper cells also stimulate phagocytes to engulf pathogens by phagocytosis.
Describe the steps of cytotoxic T cells destroying infected cell
- cytotoxic T cells binds to infected cell
- perforin makes holes in infected cells membrane, damages membrane
- infected cell lyses
Describe the steps of humoral immunity (B lymphocytes)
- B cells contain many different protein receptors on them - one will be complementary to a antigen
- B cell processes the antigen and presents them on its surface (becomes Antigen presenting cell)
- Activated Helper T cell attach to processed antigens on B cells thereby activating B cells to release cytokines (there are many activated T helper cells as mitosis has occurred)
- The B cell is now activated to undergo clonal selection via mitosis
- The cloned plasma cells produce and secrete the specific antibody that exactly fits the antigen on the pathogen surface.
- The antibody attaches to antigens on pathogen and destroys them - also cause agglutination
- Some B- cells are memory cells. These respond to future infections by the same pathogen by dividing rapidly and developing plasma cells that produce antibodies. This is secondary immune response
Describe the primary immune response
- occurs when an antigen comes in contact to the immune system for the first time. During this time the immune system has to learn to recognize antigen and how to make antibody against it and eventually produce memory lymphocytes
Describe the secondary immune response
- occurs when the second time (3rd, 4th, etc.) the person is exposed to the same antigen. At this point immunological memory has been established and the immune system can start making antibodies immediately
Define pathogen
- a microorganism that causes disease and an immune response
When a pathogen causes an infection, plasma cells secrete antibodies which destroy this pathogen.Explain why these antibodies are only effective against a specific pathogen.
- Antigens (on pathogen) are aspecific shape /have specific tertiary /3D structure;
- Antibody fits /binds /is complementary ot antigen /antibody-antigen complex forms;
The diagram shows an antibody molecule. What is the evidence that this antibody has a quaternary structure?
- includes four polypeptide chains
Scientists use this antibody to detect an antigen on the bacterium that causes stomach ulcers. Explain why the antibody will only detect this antigen
- Antibody / variable region has specific amino acid sequence / primary structure;
- tertiary structure of the binding site is complementary to / fits / binds with these antigens;
- Forms complex between antigen and antibody;
State the differences between primary and secondary immune response
- primary response occurs as a result fo primary contact with an antigen whereas secondary response occurs as a result of second and subsequent exposure of
the same antigen - primary responding cells is naïve B-cell and T-cell where as secondary responding cells is memory cells
- in primary response, Lag phase is often longer (4-7 days), sometimes as long as weeks or months.whereas in secondary response, Lag phase is shorter (1-4 days) due ot the presence of memory cell
- in primary response, Level of antibody reaches peak in 7 to10 days whereas in secondary response, Level of antibody reaches peak in 3 to 5 days
- in primary response, It takes longer time to establish immunity whereas in secondary response, Takes shorter time to establish immunity
- in primary response, Amount of antibody produced depends on nature fo antigen. Usually produced in low amount whereas in secondary, Usually 100-1000 times more antibodies are produced
- in primary response, Antibody level declines rapidly whereas in secondary response, Antibody level remain high for longer period.
Define monoclonal antibody
- a single pure type of antibody produced by a single clone of plasma cells
What are the uses of monoclonal antibodies?
- Targeting specific cell types - targeted
medication (eg. Cancer) - Pregnancy testing
- Medical diagnosis - linked to ELISA
(identify presence and concentration of an antigen or protein)
Describe how to make monoclonal antibodies
- purified protein is injected into animals (often rabbits or mice)
- they produce antibodies that can be collected in the blood of the injected animal
- serum is then purified to remove non-specific antibodies that don’t bind to the injected protein
What are the two types of monoclonal antibody therapy?
- direct monoclonal antibody therapy
- Indirect monoclonal antibody therapy (magic bullets)
What is an example of direct monoclonal antibody therapy?
- herceptin in the treatment of breast cancer
Describe direct monoclonal antibody therapy
- Monoclonal antibodies are produced specific to the antigens on cancerous cells
- The antibodies are given to a patient
- The antibodies attach to the antigens on the surface of the cancer cells & prevent their uncontrolled growth
Describe indirect monoclonal antibody therapy (magic bullets)
- A cytotoxic drug (a drug that kills cells) is attached to the monoclonal antibodies
- The antibodies are given to the patient
- When the antibodies attach to the antigens on the cancer cells it kills them
Summarise how direct monoclonal antibody works
- Blocks chemical that stimulates uncontrolled mitosis
What is the advantage of direct monoclonal antibody?
- Highly specific
- Non toxic
Summarise how indirect monoclonal antibodies work
- drug kills the cancer cells
What are the advantages of indirect monoclonal antibodies?
- Smaller doses of drug target specific sites (therefore cheaper)
- Less side effects from the drug
Describe the use of monoclonal antibodies in pregnancy/lateral flow tests
- reaction between (HCG/antigen) and monoclonal antibody at the reaction site (test strip)
- HCG (antigen) antibody complex gets trapped in second fixed antibody test site, causing a line
- If no HCG, not fixed and swept to control site
What is the purpose of the control site?
- ensures test working
Why does lateral flow test or pregnancy test cause a coloured line?
- dye is attached to antibodies so antigen antibody complex is visible if present
Describe the steps of an ELISA test
- Antigens from the sample are attached to a surface (usually a multi-well plate), time is then given for the antigen to adhere to the plate *can coat with antibody and add specific antigen instead
- Remove unbound antigen (or antibody)
- A specific antibody is applied to the surface so that it can bind with the antigen
- Remove unbound antibody (or antigen)
- Another antibody is added which is linked to an enzyme
- Remove unbound antibody linked to enzyme (or antigen)
- substance containing the enzyme’s substrate is added. The subsequent reaction produces a detectable signal, most commonly a colour change. The higher the concentration of antibody, the stronger the colour change, which can then be detected by a spectrometer
Why does ELISA test cause colour change?
- When the antibody recognises and binds to the protein in solution, the attached enzyme causes a colour change
What does the amount of colour change in an ELISA test depend on?
- amount of antibody that bound to the protein in the sample (ie the more the colour changes the higher the concentration of the antigen)
What is the ELISA test used for?
- detect HIV
- detect pathogens of diseases including tuberculosis and hepatitis
- drug test
- allergen test
What are the advantages of an ELISA test?
- useful where the quantity of an antigen needs to be measured so useful in drug and allergen tests to determine concentration
What are the ethical issues with the use of vaccines and monoclonal antibodies?
- Production of monoclonal antibodies involves the use of mice – used to produce antibodies and tumour cells. Animal right issues here
- Must be tested on humans: Clinical trials needed
- Risk of immune system reaction when given to patients and need informed consent from patient
What is a vaccination?
- An introduction of appropriate disease antigens into the body: e.g dead form of microorganism Attenuated (harmless version) Surface antigen
Why do vaccines trigger cell mediated immunity?
- contain antigens
Define herd immunity
- the resistance to the spread of a contagious disease within a population that results if a sufficiently high proportion of individuals are immune to the disease, especially through vaccination
How does a vaccine make someone immune to a pathogen?
- (Vaccine contains) antigen / attenuated/dead/inactive pathogen;
- (Specific) helper T cell stimulates B cell specific to antigen;
- B cell clones/divides by mitosis;
- Plasma cells release antibodies;
- Memory cells produced meaning higher concentration of antibodies/antibodies produced faster in secondary response/on infection with the actual pathogen;
What are the potential problems with vaccines?
- Killing/inactivation process may fail and microorganism remains pathogenic;
- Attenuated microorganism might mutate and become harmful;
- Non-pathogenic microorganism may mutate and harm cells;
- Genetic material / protein in vaccine may harm cells;
- Vaccine might not be effective against all strains of a pathogen;
- Allergic reactions to vaccine ingredients;
- Vaccine could be accidentally contaminated with an unrelated pathogen;
- People may test positive for a disease after vaccine used (even though they don’t have the disease). E.g. antigen in vaccine may lead to test giving “false positive” for disease. This may affect a person’s work/life;
Why is HIV a virus?
- it is acellular and non living
Why is HIV a retrovirus?
- contains RNA and reverse transcriptase
Draw and label the structure of HIV
- genetic material (RNA)
- reverse transcriptase enzyme
- lipid envelope
- capsid
- attachment proteins
Define acellular
- not a cell, doesn’t contain organelles
Define non living
- cannot reproduce by itself
Describe how HIV infects T helper cells
- Attachment proteins on HIV virus bind to protein receptors on the host T helper cell
- Genetic material (RNA) of the HIV virus enters host T helper cell where reverse transcriptase takes place to turn single stranded RNA into single stranded DNA
- Single stranded DNA is formed into double stranded DNA and integrates into the host cells DNA
- The hosts enzymes and ribosomes are used to produce viral genome RNA and viral HIV proteins such as the capsid, attachment proteins and reverse transcriptase enzyme
- The viral genome RNA and viral HIV proteins are assembled into the new viruses
- New virus exits host cell by the process of budding which coats the virus in the phospholipid bilayer from the host cell surface membrane to form lipid envelope on the new virus
Why are antibiotics ineffective against viruses?
- viruses don’t contain cell walls like bacteria and rely on the host for metabolic activities so there are no metabolic activities to inhibit as antibiotics inhibit murein formation and ultimately, the formation of cell walls
Describe the structure of the human immunodeficiency virus (HIV)
1 RNA (as genetic material);
2. Reverse transcriptase;
3. (Protein) capsomeres/capsid; 4. (Phospho)lipid (viral) envelope
State the similarities of HIV and bacterium
- both contain RNA
- both contain enzyme molecules
State the differences of HIV and bacterium
- Bacterium contains cell walls whereas HIV doesn’t
- HIV contains capsid whereas bacterium doesn’t
How does HIV cause symptoms of AIDS?
- minor infections of mucous membranes and recurring respiratory infections
- as AIDS progresses, number of immune system cells decreases further and serious infections (chronic diarrhoea, severe bacterial infections and tuberculosis) occur
- late stages (toxoplasmosis of brain, candidiasis of the respiratory system)
Why is standard deviation used?
- Gives an indication of the range of valves either side of the mean.
- Gives an indication of the spread of data, and how far values are from the mean
Why does it mean if the standard deviation is smaller?
- the data is more reliable as the values are closer to the mean
What does it mean if the standard deviation of two different mean overlap?
- There is no significant difference between the two sets of data
What does it mean if the standard deviation of two different means do not overlap?
- There is a significant difference between the two sets of data
What is the student t test used for?
- is used to judge the significance of any difference between the means of two sets of data at a probability level (in biology we look at 0.05/5%)
What is S in student t test formula?
- Standard deviation
What is X in student t test formula?
- mean
What is N in student t test formula?
- number sampled
Which formula for the degrees of freedom?
- (n1-n2)-2
Null hypothesis
- there is no statistically significant difference between the two sets of data. (T- test between two means)
- Any difference is due to chance alone. The probability of obtaining this difference by chance is greater than 0.05
Hypothesis
- There is a statistically significant difference between the two sets of data i.e. The probability of obtaining this difference by chance is less than 5%. (p=0.05)
What is p-value?
- probability value
What does it mean if your p value for degrees of freedom is less than or equal to 0.05?
- there is a significant difference between the means samples. The probability of obtaining this difference by chance is less than 5%.
What does it mean if your p value for degrees of freedom is more than 0.05?
- there is no statistical difference between the means. The probability of obtaining this difference by chance is greater than 5%.
Describe the aseptic techniques
- Sterilise all equipment - dip in methanol and pass through blue flame - to ensure no unwanted bacteria grow thus prevent contamination on bacteria culture plate
- Wipe bench with distenfant - to remove any unwanted bacteria
- Open lid of petri dish as little as possible (slant) - prevent unwanted bacteria entering agar plate
- Wash hands with soap- prevent contamination of bacteria from hands
- Use sterile pipette - ensure no contamination of broth culture to agar plate
- Flame neck of culture bottle - ensure pure culture and prevent contamination
- Agar is sterilised - to kill any bacteria and so only one type of bacteria (desired bacteria) is on the agar plate.
- Work in an area that upward convection current (use of bunsen burner)= ensure area work in is free free from contamination
Define aseptic technique
- Aseptic technique means using practices and procedures to prevent contamination from other bacteria/ pathogens.
Describe how to flood agar plate with bacteria (produce a bacterial lawn with aseptic techniques)
- Sterilization of all equipment wash hands with soap and disinfect the work surface - prevent contamination
- Transfer broth culture to agar plate by sterile pipette
- ensure that broth culture bottle is flamed before and after opening
- only partly open lid of agar plate when pipette liquid broth on agar - Sterilize glass glass spreader (methanol and flame) and then use the spreader to spread bacteria over the plate
Give two reasons why it would be important to use sterile techniques during this investigation
- To prevent contamination of apparatus with other microorganisms / bacteria;
- To prevent personal contact with bacteria;
- To prevent release of bacteria into air;
The antibiotic reached the bacteria by diffusion. Suggest why an effective antibiotic may produce only a small clear zone.
- it diffuses slowly
Why is antibiotic X most useful for treating gonorrhoea?
- produces inhibition zone greater than the minimum diameter
Why did the student use a maximum concentration of disinfectant of 40%?
- Clear zone would be too large OR Clear zones would overlap/merge OR Could kill all bacteria on the plate;
Suggest two variables the student should control in using first paper discs in this investigation
- Same size / area / thickness;
- Same material/absorbency;
- In solution for same time period;
Explain why there is a clear zone around each paper disc
- Bacteria are killed;
Explain why she passed forfeits through a Bunsen flame before and after each time she used them
- To sterilise/kill bacteria;
- So that only one kind of bacteria present
on agar plate/to prevent contamination by bacteria;
Explain the appearance of the agar plates after incubation
- Clear zone / inhibition zone is where bacteria have been killed;
- Antibiotic diffuses out of paper disc into agar;
- Bacterium A killed by tetracycline/tetracycline has little effect on bacterium B;
- Bacterium B killed by penicillin/bacterium A resistant to penicillin;
- Both kinds of bacteria resistant to streptomycin;
Why was the agar sterilised in the start of the investigation?
- to ensure that no unwanted bacteria will be present;
Water was added to plate 2 as control. Explain why this control was necessary.
- to check that bacteria cells do not die anyway to show water has no effect on growth;
Explain why some bacteria were able to grow on plate 1
- some bacteria are resistant
- some areas of dish have no antibiotic /
antibiotic not spread evenly;
A student used a serial dilution to investigate the number of cells present in a liquid culture of bacteria. Describe how he made a 1 in 10 dilution and then used this to make a 1 in 1000 dilution of the original liquid culture of the bacteria
- Add 1 part bacteria culture to 9 parts (sterile) liquid to make 10^-1 dilution;
- Mix (well);
- Repeat using 9 parts fresh (sterile) liquid and 1 part of 10^-1 and 10^-2 dilutions to make 10^-3 dilution; OR Add 1 part 10^-1 (suspension) to 99 parts (sterile) liquid to make 10^-3 dilution;
A student used a serial dilution to investigate the number of cells present in a liquid culture of bacteria. The student looked at cells in the 1 in 10 dilution during his preliminary work. He decided
Not to use this dilution to determine the number of cells in the undiluted liquid culture. Suggest an explanation for this students decision
- Count unlikely to be accurate / repeatable / reproducible / reliable;
- Because too many cells; OR Because cells overlapping / not spread out;
What is the role of disulphide bridge in forming the quaternary structure of an antibody?
- bonds the two polypeptide chains together to form a quaternary structure
Why HIV controllers do not develop symptoms of AIDS?
- HIV controllers have a greater number of helper T cells
- which are used in immune responses
- helper T cells bind to more antigen presenting cells which turn into plasma cells
- for secreting antibodies
Natural active immunity
- following infection and creation of bodies own antibodies and memory cells
Artificial active immunity
- following the introduction of a weakened version of the pathogen or antigens via a vaccine
