BLD434 Section 5

Question 1

AIDS

Answer 1

Acquired Immune Deficiency Syndrome
- AIDS due to HIV is a secondary infection

Question 2

gp41 and gp120

Answer 2

Glycoproteins on virion that form spike protein that bind to CD4 on target cell membranes. gp41 = stem; gp120 = bulb

Question 3

Macrophage-tropic HIV strain

Answer 3

Comes first
Generally initiated at mucosal sites of entry by binding co-receptor CCR5 and preferentially infect macrophages and DCs

Question 4

Lymphocyte-tropic HIV strain

Answer 4

Binds CXCR4 and infects CD4+ T cells
Progresses, leads to AIDS

Question 5

Reverse transcriptase

Answer 5

Copies RNA into cDNA after HIV injects the host cell with its RNA genome

Question 6

Integrase

Answer 6

Splices HIV cDNA into the host cell genome and it just sits there - Quiescence provirus (latent)

Allows for a permanent stable infection of a host cell because while the person is always HIV+ they aren’t always having symptoms.

Question 7

Acute HIV Syndrome

Answer 7

Phase occurs 4-8 weeks after initial exposure to HIV. Person will be highly contagious and will only sometimes develop flu-like symptoms.

Question 8

Why do CD4+ T cell numbers plummet during end of acute infection stage of HIV, and then partially rebound?

Answer 8

They get killed by CD8+ Tc. They rebound due to new production of naive CD4+ T cells in the thymus.

Question 9

Combination Antiviral Therapy (ART) vs single drug therapy for HIV

Answer 9

ART is used to destroy entire populations of viruses before they accumulate enough to mutate to resist all the drugs.

Question 10

What characteristics of HIV make it difficult to create an effective vaccine against HIV?

Answer 10

• High mutation rate of HIV genome
• Must target both CD8+ T cell response and mucosal Ab response to be effective
• HIV remains latent as provirus integrates into host genome and can reactivate later

Question 11

Serology

Answer 11

The study of non-cellular components in blood`

Question 12

EIA

Answer 12

Enzyme Immunoassay
- Plastic wellss w fixed Ab or Ag to detectt Ag-Ab reactions. Produces a colored product

Question 13

Window period or eclipse

Answer 13

The time between exposure and presence of detectable serum Ab
- False negatives can occur here

Question 14

Sensitivity

Answer 14

Measures the percentage of real positives that are identified as positive results.

Question 15

Specificity

Answer 15

The percent of negatives that are correctly identified as negatives.

Question 16

What are the 2 main analytes that can be measured in serological tests for infectious disease?

Answer 16

Patient Ab & viral Ag

Question 17

Testing Algorithm for HIV

Answer 17

1. Screening: HIV-1/2 Ag/Ab combination immunoassay
2. Confirmatory: (if screen +) HIV-1/2 Ab differentiation immunoassay
   - Can detect 1, 2, or both, or be negative for both (go to 3)
3. Discrepant results test: HIV-1 NAT (b/c most popular in US)

*High risk adult would get immediate viral Ag nucleic acid testing

Question 18

What are the drawbacks of early detection EIA tests for HIV diagnosis? How has 4th gen EIA limited these?

Answer 18

Large window period (45 days) giving false negatives. Also, false positives due to human cell contaminants. And cannot detect HIV-2

4th gen has shorter window period (14 days) and can detect both HIV-1, HIV-2, and p24. Still has some false positives tho.

Question 19

Confirmatory tests for HIV

Answer 19

Western Blot & NAT (nucleic acid test)

Question 20

What is the preferred method for detecting HIV in newborn infants? Why does this differ from the usual?

Answer 20

Test for viral nucleic acid via qualitative PCR, for either
1. HIV cDNA in mononuclear cells
2. HIV virion RNA in plasma

Adult screening can’t be used because passive IgG from mom in baby’s serum can cause false positives for up to 18 months old. Also, baby’s IgM to HIV lacks specificity; not adequate for testing.

Question 21

HIV viral load

Answer 21

Measures the amount of HIV viral RNA in the patient blood sample.
Increase = drug resistance
Decrease = successful drug therapy

Question 22

What laboratory test monitors progression from HIV to AIDS?

Answer 22

CD4+ T cell count (flow cytometry)
Test can read 3 things to be indicative of AIDS; only need 1:
1. Absolute T cell count <200/micro
2. CD4 T cell % (of total lymphocytes, <14%)
3. CD4:CD8 ratio (<1:1, reference is 2:1)

Question 23

Fecal-oral route

Answer 23

Transmission via contaminated food/water (ex: HAV, HEV)

Question 24

Parenteral route

Answer 24

Transmission via blood/body fluids (ex: HBV, HCV, HDV)

Question 25

IgM Ab in viral staging

Answer 25

Presence indicates current or recent
- In a newborn, this indicates congenital infection (from mother)

Question 26

IgG Ab in viral staging

Answer 26

Presence indicates current or past infection & immunity to re-infection

Question 27

Viral Ag or Viral DNA or RNA in viral staging

Answer 27

Positive serological tests indicate current infection

Question 28

Assays in patient serum for acute hepatitis panel

Answer 28

Hep A = IgM anti-HAV
Hep B = IgM anti-HBV and HBsAg
Hep C =