5. the immune system

• what do white blood cells do?

  they work toidentify:-pathogens- cells from another organism of the same species-abnormal self-cells(eg. cancer cells)-toxins(types = lymphocytes/phagocytes)
• what is an antigen?

  - a toxin orforeign moleculewhichtriggers an immune responsewhich produces antibodies against them- arePROTEINSeach w/ a specific tertiary structure
• what is a non-specific immune response?

  - response isimmediate+ thesame for all pathogens- involvesphysical barriers(eg. skin)- involves phagocytes
• what is a specific immune response?

  - response isslowerbut longer lasting + isspecific to each antigen- involvescell mediated responses(T-cells)-humoral response(B-cells) (antibody production)
• how does the body know which cells are your own + which aren't?

  proteins (w/ specific tertiary structures) found on cell surfaces allows immune system to identify + distinguish between:

  - pathogens + toxins they produce

  - non-self (foreign) cells from organisms of same species

  - abnormal cells (ie. cancer cells)
• what is phagocytosis?

  - thebreakdown of pathogensby phagocytes before pathogens cause harm- pathogens ENGULFED within VESICLES which contain enzymes + DIGESTED
• what is the process of phagocytosis?

  - Phagocyterecognisesforeign antigen-Cytoplasmof phagocyte moves around it- Pathogen trapped inphagocytic vacuole- Lysosomefusewith vacuole- Releaselysozymeswhichhydrolysethe pathogen- Phagocyte thenpresentsthe antigens
• what are B-lymphocytes (B-cells)?


  - arise from stem cells in bone marrow- mature inBONE MARROW-PRODUCE ANTIBODIES-responds to foreign material OUTSIDEbody cells including bacteria + viruses
• what are T-lymphocytes (T-cells)?

  - arise from stem cells in bone marrow- mature inTHYMUS GLAND- DO NOT produce antibodies-responds to foreign material INSIDEbody cells (such as those altered by viruses or cancer/ also responds to transplanted tissues)
• what is cellular response?

  Uses T-lymphocytesT-lymphocytes circulate the body in the blood until it meets an antigen it has the receptor site forTypes of T-lymphocyte:Killer T-cells– cause lysis of target cells, will destroy virus infected or cancer cells.Helper T-cells– activate B-lymphocytes to produce antibodies.
• what is activation of helper T-cells (Th)? (cell mediation)

  - helper T-cells haveRECEPTORS(complimentary in shape) thatBIND TO PRESENTED ANTIGEN- thisactivateshelper T-cell STIMULATING MITOSIS to produce clones of cytotoxic T-cells + phagocytes
• what are the consequences of producing clone T-cells in cell mediation?

  1- stimulates furtherPHAGOCYTOSIS2- production ofCYTOTOXIC T-CELLS(Tc) which produce the protein perforin - cell dies as result3- production ofMEMORY T-CELLSwhich remain in blood + tissue fluid, ready to respond in future infections4- other main effect isB-CELL ACTIVATION
• what is the humoral response?

  - B-cells w/ antibodies on their outer surface r already present in blood

  - they will bind to an antigen with a specific, COMPLIMENTARY shape to the antibody, the 2 attach to one another + antigen is taken into the cell via endocytosis

  ('humoral' = fluids ie. blood/ tissue fluid)

  
• what is antigen presentation + activation of B-cells? (humoral immunity)

  - B-cells process the antigen + present them on their outer surface. The cells bind antigen activating the B-cell
• what is the primary immune response? (humoral immunity)

  - activated B-cell divides by MITOSIS to form a CLONE of plasma B-cells - process called CLONAL SELECTION

  - these clones only survive a few days but produce LARGE AMOUNTS OF ANTIBODIES SPECIFIC to the invading pathogen

  
• what is the secondary response? (humoral immunity)

  - MEMORY CELLS produced that REMAIN after infection + provide LONG TERM IMMUNITY.

  - they circulate in blood + tissue fluid + DIVIDE RAPIDLY INTO PLASMA CELLS TO PRODUCE ANTIBODIES when pathogen next encountered

  
• what are antibodies?

  - a protein produced by lymphocytes (B-cells) in the presence of a specific antigen (also known as immunoglobulins - lg)

  (each antibody designed for interacting w/ a SPECIFIC antigen)

  (proteins w/ quaternary structure)

  
• what are the 2 ways that antibodies work?

  - AGGLUTINATION = bind antigens + clump them together, making it easier for phagocytes to locate, engulf + disable pathogens

  - PHAGOCYTOSIS = bind to pathogens, constant part is recognised by phagocytes which engulf the 'marked' pathogen

  (antibodies prepare the antigen for destruction - don't destroy them themselves)
• what are monoclonal antibodies?

  - 'MONO' meaning one/ 'CLONAL' meaning form of a clone

  - SPECIFIC ANTIBODIES PRODUCED FROM A CLONE OF CELLS, DERIVED FROM A SINGLE CELL

  - highly specific, purified sample of single antibody, produced outside body - recognises ONLY 1 ANTIGEN
• why are monoclonal antibodies produced?

  because B-cells are shorted lives + can only divide in living organisms so poses many problem
• what are monoclonal antibodies used in?

  - detect HIV

  - target treatment of cancer cells

  - identify pathogens

  - ELISA (enzyme-linked immunosorbent assay) testing

  - detect drugs in urinalysis

  (-more)
• How are monoclonal antibodies used to treat cancer?

  - produced specific to antigens on cancer cells

  - these antibodies given to a patient + attach to receptors on cancer cells

  - attach to surface of cancer cells + block chemical signals that stimulate uncontrolled growth

  (can carry anti cancer drugs on them when they bind to the cancer cell - indirect monoclonal antibody therapy)

  (fewer side effects than other cancer treatments)

  
• what is ELISA testing?

  - ELISA testing carried out to determine if someone has antibodies against a certain antigen

  - shows if they have ever encountered the antigen

  - shows if they are infected w/ the pathogen

  - shows if the concentration of antibodies for a certain antigen is in their blood

  (- commonly used to detect HIV (HIV pos. if antibodies against it is detected)
• how are monoclonal antibodies used in ELISA testing?

  - monoclonal antibodies IMMOBILISED + sample (saliva/urine/blood) passed over them

  - antigen + antibody BIND TOGETHER

  - another antibody labelled w/ enzymes is added + binds to antigens (which r bound to immobilised antibodies)

  - IMMOBILISED ENZYME CAUSES COLOUR CHANGE reaction when substrate added

  - intensity of colour change INDICATES CONC. OF ANTIBODY present

  
• how are monoclonal antibodies used in diagnoses?

  - use in directly treating cancer (eg. Herceptin)

  - detection of infection, hepatitis, chlamydia

  - detecting human chorionic gonadotrophin (hCG) in preg. tests (hcg binds to antibodies + coloured)

  
  

  (- detection of antibodies for HIV)

  (- detection of a specific cardiac enzyme to diagnose myocardial infarction (heart attack))

  (- targeting specific anti-cancer drugs to tumour cells)

  (- transplant tissue typing (can stop own cells from rejecting tissue))
• what are the ethical consideration surrounding monoclonal antibodies?

  - mice r used + they deliberately induce them w/ cancer = harmful

  - some deaths associated w/ this treatment in multiple sclerosis (MS) = patients have to have full informed consent

  - issues w/ drug trails = previous examples where people have greatly suffered (organ failure)

  (avoid arguments leaning towards 'playing god' - give general arguments supported by factual biology)
• what is a vaccine?

  the injection of a weak/ dead pathogen (in order to trigger an immune response)

  - given orally or by injection

  (weak sample/ dead sample/ subunit of microorganism/ product of microorganism -eg. toxin)
• what are the steps of a vaccination?

  1- injection of weak/dead pathogen

  2- antigens on surface of pathogen trigger immune response by LYMPHOCYTES (B + T cells)

  3- some lymphocytes remain in blood as MEMORY B-CELLS. help fight future infection by realising MORE ANTIBODIES AT FASTER RATE

  4- lymphocytes release antibodies which bind to antigens + help destroy pathogen - targeting them directly or marking them allowing PHAGOCYTES TO ENGULF THEM

  5- in future, if infected w/ pathogen, body ALREADY HAS ANTIBODIES, this faster recognition process will help CONTROL SPREAD OF DISEASE + OFFERS LONG TERM IMMUNITY
• how do vaccines affect the concentration of antibodies in the blood?

  1- vaccine given (no antibodies)

  2- antibodies INCREASE in number

  3- WBC are FIGHTING + DESTROYING pathogen

  4- antibodies on MEMORY CELLS REMAIN in blood (conc. of antibodies drop slightly as b-cells die)

  5- infected for real (some antibodies already present)

  6- memory cells produce THOUSANDS of antibodies RAPIDLY to help kill pathogen

  
• what is herd immunity?

  - INDIRECT PROTECTION from (some) infectious diseases that can occur when a SUFFICIENT PERCENTAGE of population has become immune to an infection.

  - When a very large proportion of population has been vaccinated against a single pathogen, it becomes difficult for that pathogen to spread
• why is it difficult for the pathogen to spread when there is herd immunity?

  - it is not likely you are going to meet an infected person

  - transmission is interrupted

  - those who are not immune are protected (eg. very old/ very young/ pregnant women/ immuno-comprimsed people)
• what are the types of immunity?

  - ACTIVE = when u make antibodies + memory cells against a pathogen. SLOW to develop but LONG LASTING (not always due to vaccine)

  - PASSIVE = immunity from receiving READY-MADE antibodies that come from an external source, (eg. another person). No memory cells produced - SHORT LASTING BUT IMMEDIATE (no direct contact w/ pathogen)

  - NATURAL = naturally acquired immunity (obtained through usual circumstances

  - ARTIFICIAL = received by external means (person usually asymptomatic)
• examples of types of immunity

  - ACTIVE NATURAL - infection (make antibodies urself)

  - ACTIVE ARTIFICIAL - vaccination (make antibodies urself)

  - PASSIVE NATURAL - breast-feeding (udon't make antibodies)

  - PASSIVE ARTIFICIAL - receiving anti-toxin (u don't make antibodies)
• what makes a successful vaccination programme?

  - few side effects

  - can be administered at appropriate time

  - can cause herd immunity

  - economically available in sufficient quantities to immunise most of vulnerable population

  - able to be produced, stored + transported correctly
• what makes an unsuccessful vaccination programme?

  - inability to produce immunity (for certain people -eg. people w/ defective immune systems)

  - too many varieties of the pathogen to produce an effective vaccine = ANTIGENIC VARIABILITY - spontaneous mutations of pathogen, so diff. antigens not recognised by immune system

  - objections of medical, religious, or ethical reasons

  - if pathogens can 'hide' from immune system (eg. inside body cells)

  - disease may be caught before vaccine becomes effective
• what are the ethical issues of vaccines?

  - often involves animal testing

  - have side effects which could cause long term harm

  - on whom vaccines should be tested on, how trials should be carried out, + how much risk participants r put under should be considered

  - should vaccines be trailed w/ unknown health risks

  - should vaccines be compulsory or not

  - cost of vaccine programmes
• what is the structure of HIV virus?

  - human immunodeficiency virus (causes disease AIDS - acquired immune deficiency syndrome)

  - lipid envelope with attachment proteins embedded

  - capsid enclosing 2 single strands of RNA + some enzymes

  - reverse transcriptase enzyme - catalyses the production of DNA from RNA (because of this HIV belongs to a group of viruses called retroviruses)

  
• how is HIV replicated in helper T cells?

  - Attachment proteins attach to a receptor molecule on a T-helper cell

  - Capsid released into cell - released genetic material into cells cytoplasm

  - Reverse transcriptase is used to make a complementary strand of DNA from RNA - inserted into human DNA

  - Host cell enzymes are used to make viral proteins from viral DNA

  - Proteins assembled into new viruses

  - Bud from cell then infect others

  
• how does HIV cause the symptoms of AIDS?

  - causes AIDS by killing/ interfering w/ normal functioning of helper T cells

  - less T cells means immune system can't stimulate B cells to produce antibodies (memory cells also infected + destroyed)

  - body can't produce immune response + becomes susceptible to other infections + cancer
• how is ELISA testing used for HIV?

  - ENZYME-LINKED IMMUNOSORBENT ASSAY

  (- uses antibodies to detect presence + quantity of protein present in sample)

  - HIV antigens attached to plate surface + patients blood poured over it

  - if that sample contains antibodies against HIV, those antibodies + antigens would bind together

  - 2nd antibody linked to an enzyme is added + binds to any HIV antibodies

  - substrate added + if all molecules ave attached to one another, the substrate is broken down by enzyme causing colour change (pos. result)

  (- washed multiple times to remove any unattached antigens and excess antibodies)