Human Immunodeficiency Virus (HIV)

INTRODUCTION:
  • Etiologic agent of Acquired Immunodeficiency Syndrome (AIDS).
  • Discovered independently by Luc Montagnier of France and Robert Gallo of the US in 1983-84.
  • HIV is found in Blood, Semen, Saliva
  • Leading cause of death of men aged 25-44 and 4th leading cause of death of women in this age group in the US.
  • HIV prevalence can be assessed by Sentinel surveillance
  • Oncogenic reterovirus
CHARACTERISTIC OF VIRUS:
  • Icosahedral (20 sided), enveloped virus of the lentivirus subfamily of retroviruses.
  • Retroviruses transcribe RNA to DNA.
  • Retroviruses contain an RNA genome and an RNA-directed DNA polymerase (reverse transcriptase)
  • Two viral strands of RNA found in core surrounded by protein outer coat.
  • HIV is a spherical, enveloped virus. The genome is diploid, composed of two identical single-stranded, positive sense RNA copies.
  • Outer envelope contains a lipid matrix within which specific viral glycoproteins are imbedded.
  • HIV contains Integrase , RNA directed DNA polymerase ,Ribonuclease
  • These knob-like structures responsible for binding to target cell.
  • Boiling, Ethanol, Cidex can destroy HIV in vitro
STRUCTURAL GENES:
  • Three main structural genes:
  1. Group Specific Antigen (Gag)
  2. Envelope (Env)
  3. Polymerase (Pol)
Group Specific Antigen (Gag)
  • Located in nucelocapsid of virus.
  • Codes for core HIV
  • Icosahedryl capsid surrounds the internal nucleic acids made up of p24 andp15.
  • p17 lies between protein core and envelope and is embedded in the internal portion of the envelope.
  • Two additional p55 products, p7 and p9, are nucleic acid binding proteins closely associated with the RNA.
Envelope (Env) gene
  • Codes for envelope proteins gp160, gp120 and gp41.
  • These polyproteins will eventually be cleaved by proteases to become HIV envelope glycoproteins gp120 and gp41.
  • gp160 cleaved to form gp120 and gp41.
  • gp120 forms the 72 knobs which protrude from outer envelope.
  • gp41 is a transmembrane glycoprotein antigen that spans the inner and outer membranes and attaches to gp120.
  • gp120 and gp41 both involved with fusion and attachment of HIV to CD4 antigen on host cells.
Polymerase (Pol)
  • Codes for p66 and p51 subunits of reverse transcriptase and p31 an endonuclease.
  • Located in the core, close to nucleic acids.
  • Responsible for conversion of viral RNA into DNA, integration of DNA into host cell DNA and cleavage of protein precursors.
Exam Question
  • HIV Retrovirus are RNA oncogenic virus
  • Boiling, Ethanol, Cidex can destroy HIV in vitro
  • HIV prevalence can be assessed by Sentinel surveillance
  • HIV effects CD4 cells 
  • HIV contains Integrase , RNA directed DNA polymerase ,Ribonuclease
  • HIV Belongs to the subgroup lentivirus
  • HIV is Characterised by the presence of reverse transcriptase enzyme
  • GAG Codes for core HIV
  • CD4 T cell , Macrophage, Dendritic cell are the target for initiation and maintenance of HIV infection

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