immunology Flashcards
(a) Changes to the protein coat of the influenza virus cause antigenic variability. Explain how antigenic variability has caused some people to become infected more than once with influenza viruses.
memory B / T cells do not recognise (new antigens);
antibodies previously produced are not effective
as shape not complementary to new antigen;
Describe the role of macrophages in stimulating B lymphocytes.
antigen in membrane presented to lymphocytes /
produce cytokinins;
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;
- The shape / tertiary structure of the binding site is complementary to / fits / binds with these antigens;
- Do not accept active site for this point.
- Forms complex between antigen and antibody;
Read the following passage.
Chlamydia is a bacterium. Scientists have shown that infection with chlamydia can cause heart disease in humans. Infection with the bacterium can stimulate the formation of atheroma. This can lead to a heart attack.
Other scientists have been working with mice. These scientists have suggested that chlamydia may cause heart disease in a different way. They have found a protein on the surface of chlamydia cells which is similar to a protein in the heart muscle of mice. After an infection with chlamydia, cells of the immune system of the mice may attack their heart muscle cells and cause heart disease.
2
(ii) 1. Antibodies / memory cells against chlamydia (protein / antigen) are present;
- Protein on heart (muscle) similar to chlamydia protein / antigen so T cells / antibodies (attack heart muscle cells);
Some scientists have suggested that people should be vaccinated to prevent infection by chlamydia. Evaluate this suggestion.
Prevents / reduces heart disease / attacks;
- Cheaper to vaccinate than treat heart disease;
AGAINST
- Vaccination costly;
- Don’t know frequency of chlamydia infection;
- Research in mice might not be replicated in humans / humans might have a different protein;
- Vaccine could cause heart disease or immune response against heart (muscle);
Explain why antibodies against Salmonella do not normally bind to HIV.
Antigens on HIV are different (shape);
So, antibody will not ‘fit’/not complementary (to antigen);
Receptor sites on antibody specific to one antigen;
Explain how the adaptor molecule allows anti-gal antibodies to associate with HIV.
An anti-gal antibody is a type of antibody that helps to fight infections caused
by bacteria. If a person has a bacterial infection, for example Salmonella, anti-gal
antibodies bind to antigens on the surface of the Salmonella. Not all the
anti-gal antibodies are used to fight the infection. Even after the infection, anti-gal
antibodies remain in the blood. 5
Scientists have made adaptor molecules to try to use the anti-gal antibodies
against viruses such as HIV. The adaptor molecules are proteins. Each adaptor
molecule had a receptor site to which the HIV binds. This receptor site was
similar to the receptor site on human cells to which the HIV binds. The
adaptor molecule has another site to which an anti-gal antibody will bind. 10
The scientists then investigated whether adding adaptor molecules and anti-gal
antibodies can prevent HIV entering cells. They added adaptor molecules
and anti-gal antibodies to a culture of human cells. They then added HIV
to the culture. Their results showed that 90% of the virus particles failed
to infect cells. 15
The scientists are hoping to develop a different type of adaptor molecule to use against MRSA.
(Has site with) same shape as salmonella antigen so binds
to anti-gal antibodies;
(Has site with) same shape as receptor molecule so that HIV will bind;
Binds to both molecules;
HIV infects some human cells, such as T-cells, but not others. Suggest why.
HIV binds to specific receptor;
Only present on certain cells / T-cells
Antibiotics are not used to treat viral infections, such as HIV. Explain why
Antibiotics stop metabolism, viruses don’t have metabolism;
Viruses hide in cells, antibiotics can’t reach;
Two suitable cell components antibiotics work against that
viruses don’t have;
e.g. some antibiotics work against ribosomes, that viruses don’t have
An anti-gal antibody is a type of antibody that helps to fight infections caused
by bacteria. If a person has a bacterial infection, for example Salmonella, anti-gal
antibodies bind to antigens on the surface of the Salmonella. Not all the
anti-gal antibodies are used to fight the infection. Even after the infection, anti-gal
antibodies remain in the blood. 5
Scientists have made adaptor molecules to try to use the anti-gal antibodies
against viruses such as HIV. The adaptor molecules are proteins. Each adaptor
molecule had a receptor site to which the HIV binds. This receptor site was
similar to the receptor site on human cells to which the HIV binds. The
adaptor molecule has another site to which an anti-gal antibody will bind. 10
The scientists then investigated whether adding adaptor molecules and anti-gal
antibodies can prevent HIV entering cells. They added adaptor molecules
and anti-gal antibodies to a culture of human cells. They then added HIV
to the culture. Their results showed that 90% of the virus particles failed
to infect cells. 15
The scientists are hoping to develop a different type of adaptor molecule to use against MRSA.
When HIV, anti-gal and the adaptor molecule were added to a culture of human cells, 90% of the virus did not infect human cells. (lines 12-15). Explain why.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(ii) Explain why a different type of adaptor molecule will have to be made to use against MRSA. (lines 16-17)
Adaptor molecule binds to HIV;
(This) prevents the HIV binding to the receptor;
Therefore few HIV available to infect cells;
2 max
(ii) Would need to be complementary to MRSA (antigens);
MRSA has different antigens;
But would still need to have binding site for anti-gal;
The only vaccine used against pulmonary tuberculosis is the BCG vaccine.
Scientists have carried out trials on a ‘booster’ vaccine, MVA85A. This ‘booster’ vaccine is designed to increase the immune response to the BCG vaccine. One trial involved measuring the increase in the number of memory T cells in three groups of adult volunteers following different vaccination programmes.
- Group A – injected with BCG
- Group B – injected with MVA85A
- Group C – injected with BCG and, two weeks later, injected with MVA85A
(i) Suggest two factors the scientists should have considered when selecting adult volunteers for this trial.
- ____________________________________________________________
- ____________________________________________________________
(2)
(ii) The adults in group C produced the greatest increase in the number of memory T cells. Suggest what this shows about the BCG and MVA85A vaccines.
Age;
Sex;
Ethnicity;
All healthy / not on other medication;
Not previously vaccinated / infected with TB;
Q Do not credit sample size.
Q Allow any suitable reference to health not being affected for fourth marking point e.g. smoking, ‘depressed immune system’ etc.
(ii) Contain the same antigens;
Give two ways in which pathogens can cause disease when they enter the body of their host.
Damage / destruction of cells / tissues;
Production of toxins;
The plate must be washed at the start of step 4, otherwise a positive result could be obtained when the Giardia antigen is not present. Explain why a positive result could be obtained if the plate is not washed at the start of step 4.
Enzyme / second antibody would remain / is removed by washing;
Enzyme can react with substrate (when no antigen is present);
