2.4- cell immunity

what is a pathogen, three examples and how do they cause disease?

micro organism that causes disease

bacteria, fungi and viruses

damaging host cells and releasing toxins

what is an antigen?

what are some non self antigens?

molecules, usually proteins, located on the surface of cells which generates an immune response by lympocytes which are detected in the body (involving antibodies)

pathogens, cells from other organisms of the same species, abnormal body cells and toxins

what happens in phagocytosis?

receptors on surface of phagocyte attach to antigens on pathogen

phagocyte changes shape to move around and engulf pathogen

pathogen contained within phagosome vesicle

phagosome fuses with lysosome + releases it contents

lysozome hydrolyses pathogen and destroys it

what are lymphocytes?

what is the difference between a specific and non-specific immune response?

what are the two types of specific immune response?

white blood cells involved in specific immune response

non specific- present from birth + effective against wide range of pathogens + foreign substances

specific- slower + only effective against specific pathogens; response faster after re-infection

two types: humoral + cellular

what do t lymphocytes (T cells) recognise?

What can APC’s be?

recognise non-self antigens presented on the surface of other body cells

they can be:

cells that are infected by virus

a phagocyte which has just engulfed and hydrolysed a pathogen

abnormal body cell e.g. cancer cell

what is the role of T cells in cellular immunity?

1) pathogen invade body cells or are taken in by phagocytes

2) phagocyte/infected body cell places antigens from pathogen on its surface

3) receptors on specific T cell bind to antigen as they’re complementary

4) activates T cell (helper T cell) to divide rapidly by mitosis and form clones- releases chemicals to activate other T and B cells that are specific to the antigen

what are the three different functions of T cells?

1) some are cytotoxic T cells which destroy infected body cells- produce a protein perforin- makes holes in cell membranes

2) some develop into memory cells- enables rapid response to future infections by same pathogen

3) others are helper T cells that release chemical signals which stimulate other cells e.g. phagocytes, B cells and T cells

what is the humoral response?

cell surface membranes of B cells contain specific antibodies (act as receptors)

once a specific B cell with a complementary antibody binds to an antigen, this activates the B cell

B cell then divides rapidly by mitosis to form clones (clonal selection)

antibodies are produced that are complementary to a specific antigen

develops into either plasma or memory cells

what do plasma cells do and what is this known as?

secrete antibodies directly

primary immune response

what do memory cells do and what is this known as?

if they encounter the same antigen later, they:

divide rapidly, produce large numbers of memory and plasma- more antibodies will be produced faster

secondary immune response- long term immunity

what are antibodies and what do they do? draw the structure

what happens when an antibody binds to an antigen? (after a complex is formed)

1) proteins synthesised by plasma cells (B cells)

bind to antigen forming antigen-antibody complex- complementary shapes

antibodies are therefore very specific

2) agglutination occurs- all bacteria are clumped together- can be engulfed more easily by a phagocyte

what are monoclonal antibodies?

does the antigen have to be a pathogen?

identical antibodies produced from a single clone of a B cell

no, any non-self protein will result in production of monoclonal antibodies by B cells

what are the four uses of monoclonal antibodies?

medical diagnosis

targeted drug treatments

drug testing of athletes

pregnancy testing kits

what is antigenic variability?

relate to immune response

antigens on the surface of each strain are different e.g. influenza viruses

won’t correspond to memory cells from previous infections

what does the ELISA test use?

what is the process?

uses monoclonal antibodies to detect the presence of and amount of a specific protein in a sample

container is coated with monoclonal antibodies

sampled to be tested is added + if specific antigen is present, it will bind to the antibodies

wash off unbound antibodies

a second antibody, with an enzyme attached is added- this binds to the antigens or the first antibody

the substrate for this enzyme is added- produces a colour change indicating a positive result

why are the washes needed?

remove unbound antibodies and prevent a false positive test

what would happen if there are no antigens present in the sample?

2nd antibody (with enzyme attached) won’t bind , will be washed

no enzyme to hydrolyse substrate- no colour change

what are some arguments for and against using monoclonal antibodies?

for:

treat conditions e.g cancer and diabetes

new treatments for specific conditions

against:

may test on animals

deaths when treating multiple sclerosis

what is passive immunity?

individuals acquire antibodies from an outside source

immunity is immediate, however short lived as the antibodies will be broken down and not replaced by the body

what is active immunity?

immune system is stimulated to produce its own antibodies

memory cells are produced which means antibodies can be produced again

takes longer but is longer lasting

what is vaccination?

what do vaccines contain and what do these do?

what may vaccines be?

introduction of a vaccine into an organism,

antigens and stimulates the production of specific plasma cells, antibodies and memory cells against a particular pathogen

killed or attentuated (weakened) pathogens/ isolated antigens

what makes a vaccine programme successful?

few side effects

economically available in quantities sufficient to immunise entire vulnerable population

must be easily stored and transported

must have means of administration

what is herd immunity?

vaccinating 90% of population is sufficient to stop the spread of the disease because pathogen will be killed quickly in vaccinated people and people aren’t vaccinated have a very low chance of coming into contact with another unvaccinated person

why might vaccination not eliminate a disease?

some individuals have a defective immune system

pathogen mutates quickly- change their antigens so immune system fails to recognise infection

many varieties of same organism, each with a different antigen

what are the arguments for and against vaccinations?

for:

protects against diseases

protects communities- herd immunity

against:

side effects

clinical trials on humans

animal testing

when to discontinue?

how does HIV replicate?

attachment proteins on virus binds to specific, complementary receptors on surface of helper T cells

RNA injected into T helper cell and reverse transcriptase converts RNA into DNA

DNA inserted into T cell’s genome

DNA transcribed into RNA

Viral proteins are produced (for assembly into virus particles)

how does AIDS develop and what are the symptoms?

replication and release of HIV from the T helper cell leads to destruction of the cells and the number of T helper cells decrease

less T helper cells mean that less B cells and T cytotoxic cells become activated

body’s immune response is reduced- individual more susceptible to other infections and cancers

fever, headaches, rash and diarrhea

what is used to treat HIV and why are these ineffective?

treated using a combination of antiviral drugs- often have to be changed as the virus has a high mutation rate + becomes resistant to them eventually

why can’t HIV be treated using antibiotics?

HIV is a virus and antibiotics are only effective against bacterial infections

this is because: viruses live in cell and antibiotics can’t reach them without damaging the cell

Why are antibiotics ineffective against viruses?

Antibiotics target bacteria and so viruses don’t have:

bacterial structure

Metabolic processes

cell wall