HIV infection and immune system

Question 1

Primary ID

Answer 1

Inherited/acquired - genetic basis (mutations) and are relatively rare

Question 2

Secondary ID

Answer 2

Always acquired, more common, caused by extrinsic factors (HIV, extreme age, drugs)
Cell mediated immunity

Question 3

Why is it bad not to have a thymus

Answer 3

No maturation of T cells and B cells

Question 4

Mutation disorder causing primary ID

Answer 4

Affects adaptive immunity
Leads to defect on chromosome 22 - DiGeorge syndrome
More susceptible to intracellular pathogens
Absent thymus

Question 5

Polymorphism disorder causing primary ID

Answer 5

Innate immunity
HLA disorder
Affects antigen presentation
More susceptible to viruses

Question 6

Polygenic disorder and primary ID

Answer 6

Adaptive immunity
IgA deficiency
More susceptible to some bacteria

Question 7

HIV causing secondary ID

Answer 7

Adaptive immunity affected, causes HIV infection -> AIDS -> eliminates CD4 cells -> viral/fungal/protozoa

Question 8

Extreme age causing secondary ID

Answer 8

Adaptive immunity affected -> lack of maternal antibodies -> premature baby susceptible to infection

Question 9

Drugs causing secondary ID

Answer 9

Adaptive immunity affected -> T and B cell deficiency -> cytotoxic cell damage -> opportunistic infections rise

Question 10

How does HIV infect a cell

Answer 10

gp120 binds to cd4
viral genome enters cell
reverse transcriptase catalyses ssRNA forming RNA-DNA
Ribonuclease H degrades the RNA to form dsDNA
dsDNA enters genome
Transcription factors generate proviral DNA into ssRNA
ssRNA -> cytoplasm
Ribosomes catalyse the production of precursor proteins
Virus assembled in cytoplasm
Virions bud
Mature virus infects other cells

Question 11

Which cytokine plays a key role in inflammation

Answer 11

IL-6

Question 12

HIV and CXCR4 and CCR5

Answer 12

• Chemokine receptor: CXCR4 and CCR5 which responds to chemokines to facilitate response
• HIV changes whether it attacks cells with CXCR4 or CCR5
• CCR5 antagonist used if particular HIV variant only uses CCR5 co-receptor on T cell - if it uses just CXCL4 or both then it will be useless

Question 13

Cycle of HIV killing CD4

Answer 13

HIV infects
Pyroptosis (kills CD4)
Causes inflammation
Recruits more healthy CD4 cells

Question 14

Humoral immune response

Answer 14

• Occurs later in infection so level of antibodies in acute infection is very low
• Non-neutralising antibodies to structural proteins (P17 and P24)
• Later neutralising bodies anti-gp120 and anti-binding molecules