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Microbiology ` microbiology—Virology Microbiology ` microbiology—Virology SEcTioN ii 175

HIV

Envelope proteins Diploid genome (2 molecules of RNA).
acquired through budding from The 3 structural genes (protein coded for):
host cell plasma membrane
p17: Matrix protein ƒ env (gp120 and gp41):
gp120: ƒ Formed from cleavage of gp160 to form
Docking Lipid envelope envelope glycoproteins.
glycoprotein
gp41: ƒ gp120—attachment to host CD4+ T cell.
Transmembrane p24: ƒ gp41—fusion and entry.
glycoprotein Capsid protein
ƒ gag (p24 and p17)—capsid and matrix
RNA Reverse proteins, respectively.
transcriptase
ƒ pol—Reverse transcriptase, Integrase,
Protease; RIP “Pol” (Paul)
Reverse transcriptase synthesizes dsDNA from
genomic RNA; dsDNA integrates into host
genome.
Virus binds CD4 as well as a coreceptor, either
CCR5 on macrophages (early infection) or
CXCR4 on T cells (late infection).
Homozygous CCR5 mutation = immunity.
Heterozygous CCR5 mutation = slower course.

HIV diagnosis Presumptive diagnosis made with HIV-1/2 Ag/ Western blot tests are no longer recommended
Ab immunoassays. These immunoassays by the CDC for confirmatory testing.
detect viral p24 Ag capsid protein and IgG Abs HIV-1/2 Ag/Ab testing is not recommended in
to HIV-1/2. Very high sensitivity/specificity. babies with suspected HIV due to maternally
Viral load tests determine the amount of viral transferred antibody. Use HIV viral load
RNA in the plasma. High viral load associated instead.
with poor prognosis. Also use viral load to
monitor effect of drug therapy. Use HIV
genotyping to determine appropriate therapy.
3
AIDS diagnosis: ≤ 200 CD4+ cells/mm
3
(normal: 500–1500 cells/mm ) or HIV ⊕ with
AIDS-defining condition (eg, Pneumocystis
pneumonia).

HIV-1/2 antibodies and p24 antigen combination immunoassay

Negative for HIV-1 and HIV-2
antibodies and p24 Ag

HIV-1/HIV-2 antibody
di erentiation immunoassay

HIV-1 HIV-1 HIV-1 HIV-1 or indeterminate
HIV-2 HIV-2 HIV-2 HIV-2
HIV-1 antibodies HIV-2 antibodies HIV antibodies
detected detected detected HIV-1 NAT

indicates reactive test result
indicates nonreactive test result HIV-1 NAT HIV-1 NAT
NAT: nucleic acid test Acute HIV-1 infection Negative for HIV-1

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