viral serology (HIV) Flashcards
- detects: IgG & IgM to HIV
- window period: 4-12 weeks
- immunochromatographic assays
- can be performed on whole blood, serum, oral fluid
rapid tests
stages
- 2-10 years after initial infection
- a syndrome of CD4 depletion resulting in opportunistic infections and cancers suggestive of cell-mediated immunity defects
final stage
hiv genes
p16 (viral assembly and budding)
vpu
most widely used screening test for HIV antibodies
ELISA (indirect)
generations
- detects: IgG to HIV-1
- window period: 6-12 weeks
1st generation
p24 ag & HIV ab
established infection
HIV screening tests
- ELISA
- RAPID TEST (immunochromatographic)
p24 without HIV ab
acute infection
generation
- detects: IgG to HIV-1/2
- window period: 6-12 weeks
2nd generation
hiv genes
- gp120 (binds to CD4 on T cells)
- gp41 (transmembrane protein associated with gp120)
env
stages
patient is either asymptomatic or may show lymphadenopathy
primary stage
hiv genes
- p66 (subunit of reverse transcriptase; degrades original HIV RNA)
- p51 (subunit of reverse transcriptase)
- p31 (integrase: mediates integration of HIV DNA into host genome)
- p10 (protease that cleaves gag precursor)
pol
first Ab to be detected; persist throughout the infection
anti-gp41
generation
- detects: IgG & IgM to HIV-1/2
- window period: 3-4 weeks
3rd generation
marker
- detecable shortly after IgM
- gradual inccrease in titer over several months
- long lasting
IgG ab
hiv
normal CD4:CD8 ratio (?), in AIDS patients (?)
- 2:1
- 0.5:1
- detects Ab to HIV
- sensitivity & specificity comparable to western blot
- not frequently used
- expensive, subjective
IFA
generation
- detects: IgG & IgM to HIV-1/2 & p24 ag
- window period: 2 weeks
- currently not approved for screening blood donors
4th generation
marker
detecable within days of infection
viral RNA
CD4 T-CELL COUNT
- HIV infects CD4 cells
- (?)/uL defines AIDS according to CDC
- also used to monitor (?)
- perform every (?) to (?) months
- (?) is the gold standard
- <200
- therapy
- 3, 6
- flow cytometry
the nine genes of HIV
- gag
- env
- pol
- tat
- rev
- nef
- vpu
- vpr
- vif
hiv genes
p19 (transports viral mRNA to the cytoplasm of the host cell)
rev
when HIV replication occurs, the (?) cell is killed
CD4
stages
- this state is known as the ARC (aids-related complex)
- quantitative T cell deficiencies with inverted CD4:CD8 ratio
intermediate stage
- detects Ab to HIV
- traditional confirmatory test but not as sensitive as 4th-gen EIA or NAAT
- interpretation is controversial but most labs report pos if at least 2 of the following 3 bands are present (p24, gp42, gp120/160)
- NAAT required following neg or indeterminate results
- time-consuming, difficult to interpret
western blot
HIV CONFIRMATORY TESTS
- WB
- IFA
- NAAT
marker
- usually detectable in 2-8 weeks
- transient
- peaks in about 1-2 weeks, undetecable about 1-2 weeks later
IgM ab
marker
- core coat for nucleic acids
- detectable in 2-3 weeks
- becomes undetectable as abs develop, then detectable again in late stages as immune system fails & virus replicates
p24 ag
hiv
Composed of (?) genes encoding (?) structural and (?) regulatory proteins
- 9
- 3
- 6
hiv genes
- p17 (inner surface of envelope)
- p24 (core coat for nucleic acids)
- p9 (core-binding protein)
- p6 (bonds to genomic RNA)
gag
three subtypes of HIV-1
- M: clades (A,C,D,H,G,K, F1,F2,J), clade B (homosexual), clade A, C, E (asia and africa)
- N (non-M, non-O)
- O (outlier)
hiv genes
p27 (enhances HIV replication)
nef
hiv genes
p14 (activates transcription of HIV provirus)
tat
TEST STAGE AND MONITOR HIV
- viral load
- CD4 T-CELL COUNT
HIV-1 viral load assay
- quantitative (?) to determine plasma HIV RNA
- used to predict disease progression, determine when to start antiretroviral therapy, & monitor response to therapy
- test (?) to (?) weeks after start of therapy & then every (?) to (?) months
- NAAT
- 2, 8
- 3, 4
window period of seronegativity (no Ab production)
6-8 weeks
- detects: HIV RNA
- window period: 5 days
- not cost effective in screening in most settings
- used for screening blood donors & infants
nucleic acid amplification testing (NAAT)
hive genes
p23 (infectivity factor)
vif
- detecs HIV RNA
- qualitative test used for confirmation
NAAT
hiv genes
p15 (integration of HIV DNA into host genome)
vpr
subtypes of HIV-2
subtypes A-E
most widely used supplementary test for confirming reactive HIV ELISA Ab test
western blot assay
