Infection 1: Host genetics and infectious disease

Question 1

Give an example of a genetic disease and the infectious disease it may protect against. (1)

Answer 1

Sickle cell and malaria

Haemoglobin S allele

Question 2

Describe the process of how Duffy blood group protects against malaria (3)

Answer 2

Duffy negative people don’t have the GATA1 site mutation and cannot code for the DARC receptor so plasmodium vivax cannot get into the cell

Question 3

List 5 genes associated with malaria (2.5)

Answer 3

a-globin					HLA-B
b-globin					HLA-DRB1
Glucose-6-phosphate dehydrogenase	TNF
Spectrin					iNOS
Erythrocyte band 3				ABO blood group
Glycophorin A				ICAM-1
Glycophorin B				Complement receptor
Duffy chemokine receptor			CD40L
CD36						IFN-g receptor 1

Question 4

Does a person always become HIV+ if they are exposed to HIV(1)

Answer 4

No
Some individuals remain uninfected by HIV despite repeated exposure
Others become HIV+ but disease does not develop
Human CD4 transgenic mice could not be infected with HIV despite carrying this known receptor for HIV

Question 5

Describe the process of why someone may be resistant to HIV infection (3)

Answer 5

Resistant individuals found to be homozygous for 32 bp deletion in the CCR5 gene
Frameshift mutation and premature stop codon
Protein is not expressed at cell surface
CCR5 is a co-receptor for HIV

Question 6

List all the factors that contribute to TB (1.5)

Answer 6

pathogen
Host immune response
environment

Question 7

What are the possible outcomes after primary infection with TB? (1)

Answer 7

90% clear it and positive for TST

10% will have a poor immune response and might be TST negative.

Question 8

What risk factors would affect the immune response to TB infection? (3.5)

Answer 8

Extremes of age
Co-infection with HIV
Post-measles
Diabetes
Renal disease
Steroid therapy
Anti-TNF treatment

Question 9

how are macrophages activated ?

Answer 9

Macrophages interact with T cells in order to bring about T cell activation in target organs, and are themselves activated by inflammatory messenger molecules (cytokines) produced by the T cells. Macrophages produce toxic chemicals, such as nitric oxide, that can kill surrounding cells

Question 10

Describe briefly what IFNGR1 deficiency is (2)

Answer 10

Premature stop codon on IFNGR1 leads to absence of

transmembrane and intracellular signalling domains