HIV and AIDS

Question 1

HIV and AIDs

Answer 1

Depletion of CD4+ helper T cells over 2-10 years

Question 2

Origin of HIV

Answer 2

• 1981 LA clusters of Kaposi’s sarcoma

- approx 100yrs ago SIV infected humans –> non-human primates species jump in Sub Saharan Africa

Question 3

Kaposi’s sarcoma

Answer 3

• recurrent pneumonia, etc opportunistic infection

- direct effects of virus (wasting syndrome)

Question 4

HIV course of infection

Answer 4

• replicates in first 6 weeks of infection
• depletion of CD4+ cells
• gradual increase in virus copy no ofter that
• decrease in CD4 cells of immune system

Question 5

HIV-1 and HIV-2

Answer 5

share 40%similarity

Question 6

leads to Acquired Immuno Deficiency Syndrome -AIDS

Answer 6

• 60million affected worldwide
• HIV-1 responsible for >99% of AIDS cases in West
• HIV-2 less virulent
• may be symptomless for 10yrs

Question 7

HIV-1 = retrovirus (lentivirus)

Answer 7

-retroviridae family of viruses are:
enveloped, circular viruses, 80-100nm in diameter
-diploid +ve sense RNA genome (7-12kb), single stranded
-replication strategy: reverse transcription to generate double stranded DNA followed by integration into host genome

Question 8

HIV-genome

Answer 8

• encodes gag,pol,env (1-3) genes flanked by LTRs
• 9 genes
• additional accessory genes

Question 9

gag

Answer 9

capsid, nucleocapsid, matrix

pro - protease required for processing gag

Question 10

pol

Answer 10

reverse transcriptase , RNase H and integrase

Question 11

env

Answer 11

envelope glycoproteins

Question 12

HIV virion structure

Answer 12

• glycoproteins gp120 + gp41 (ENV) from 72 spikes on surface
• p24 capsid protein (GAG) forms cone-shaped shell
• reverse transcriptase (50 molecules) (POL)
• (+)ssRNA diploid

Question 13

morphology of HIV-1

Answer 13

circular, conical capsid, distinctive env

Question 14

HIV gp120 binds the CD4 receptor

Answer 14

HIV infects other cell types that have CD4 molecules on their surface:
B lymphocytes
macrophages
dendritic cells
brain cells

Question 15

HIV entering cells: CD4 is HIV primary receptor

Answer 15

• normal cellular function to recognise Ag in assocn with class II MHC
• trimeric Gp120 binds to CD4
• coreceptors also bind (CXCR4 & CCR5)
• conformational change occures
• membrane fusion
• HIV enters cell

Question 16

Chemokine (co) receptors

HIV

Answer 16

alpha - CXCr4

beta - CCr5

Question 17

HIV replication cycle:

Answer 17

• The HIV RNA genome is reverse transcribed into DNA (cytoplasm)
• This translocates to the nucleus
• Integrates into the host genome
• New viral RNA may be transcribed and proteins translated
• These can be packaged into particles and bud from the cell

Question 18

Life-cycle HIV

Answer 18

1 Attachment
2 Uncoating
3 Reverse transcription 
4 Circularisation
5 Integration
6 Transcription
7 Translation
8 Core particle assembly
9 Final assembly & budding

Question 19

HIV variability

Answer 19

• RT enzyme = prone to error
• error rate = 1 in 3000 nucleotides (HIGH)
• RT lacks proofreading
• polymerisation errors generate virus diversity

Question 20

Transmission HIV

Answer 20

• body fluids
• STD
• Drug abuse intravenous
• mother-baby

Question 21

ELISA screening

Answer 21

reactive= +ve result