The Body’s Defense Against HIV-Type 1 Infection, Viral Load, and Antigenic Diversity

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The Bodys Defense Against HIV-Type 1 Infection,
Viral Load, and Antigenic Diversity

• Emmanuel Jean-Jacques
• Seminar 475
• Dr. Peter Lin

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Progression of AIDS

• Most individuals infected with HIV remain disease
  free for many years.
• During this time, individuals develop antibodies
  and cytokines, maintain stable numbers of CD4
  cells, maintain strong Cytotoxic T cell (CTL)
  responses, and contain low virus load.
• At some point, the immune system fails and most
  infected individuals progress the symptoms of
  AIDS.

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Why Does the Immune System Fails?

• The interaction between HIV and other
  opportunistic infections
• Antigenic diversity is at a high level
• Differences in viral pathogenicity contributing
  to the development of AIDS
• Drug-resistant viruses

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The Correlation of HIV-1 and CD4 Receptor

• CD4 receptor is part of the membrane of T-cells.
• During HIV invasion, the gp120 proteins on the
  surface of the HIV bind to the CD4 receptors
• Fusion of the virus membrane to the immune cells
  lipid membrane occurs and the contents of the
  virus particle enter the T-cell. So the cell is
  now infected.

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The Entry of HIV into Cells
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Devising Treatments for AIDS

• Because of the unique component (gp120) of HIV.
  Scientists are trying to devise treatments for
  AIDS. Recently Scientists have tried to attack
  the virus before it infects the cells by blocking
  the gp120 proteins to the CD4 receptor

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The Development of Neutralizing Antibody Response
During HIV-1 Infection

• Basically, this means the ability of the immune
  system to inhibit virus replication by producing
  antibodies against the virus p24 and gp41
  antigens (seroconversion).
• This humoral response to these antigens produces
  a high titer of antibody response to the gp120
  region of the virus.

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Humoral Response Continued

• According to this study, HIV-1 causes a primary
  infection stage that is associated with low
  seroconversion due to high virus load. The
  individual who is infected has a series of
  influenza-like symptoms.

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The Difference Between CCR-5 and CXCR-4 Receptors

• In the past, HIV isolates have been classified
  according to the ability to induce cytopathic
  effects and have veen designated syncytium
  inducing (SI) or non-syncytium inducing (NSI).
• SI viruses are able to utilize the ?-chemokine
  receptor CXCR-4, which is expressed on naive T
  cells.

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CCR-5 and CXCR-4 Receptors Continued

• NSI viruses utilize only members of the
  ?-chemokine receptor CCR-5, which is expressed on
  memory T cells.
• Now a days viruses are classified according the
  co-receptor they utilize.
• So that means that if CCR-5 were absent from CD4
  T cells or even distorted then the virus would
  not be able to infect the cell.

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Materials and Methods Development of
Neutralizing Antibody Response to HIV-1

• A patient (HL60) with influenza-like symptoms was
  screened for HIV infection by use of four
  available tests for the detection of HIV-specific
  antibodies
• Cloning and expression of gp120 regions from the
  seroconversion samples.
• Antigenic characterization of gp120 proteins.
• Generation and Recovery of chimeric. HXB2.gp120
  viruses.
• Virus neutralization assays.

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Cloning and expression of gp120 regions from
seroconversion

• Total RNA was extracted from plasma samples, and
  the gp120 Open Reading Frame (ORFs) were
  amplified using RT-PCR.
• The gp120 ORFs were sequenced with primers.
• Amino acid numbering was based on the HXB2 gp120
  sequence.

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Results

• Monitoring the seroconversion process

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Antigenic Characterization of gp120 proteins

• Soluble gp120 proteins taken from patient (HL60)
  sera were tested for their ability to bind a pool
  of
• HIV-positive human sera
• soluble CD4-Immunoglobulin (sCD4-Ig)
• monoclonal antibodies

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Results

• Antigenic characterization of gp120 proteins

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Generation and Recovery of chimeric HXB2.gp120
viruses

• Three of the virus clones (pCDNA3) from the
  previous test expressing gp120 and capable of
  binding sCD4-Ig were chosen for transfer into
  pHXB2-MCS vector.
• These vectors were transfected into HEK cells
  (cocultured with PHA-stimulated peripheral blood
  lymphocytes (PBL)).
• The viruses were used to infect U87.CD4 cells
  that expressed a range of chemokine receptors and
  antibodies to p24 antigens.

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Results

• Generation and recovery of chimeric HXB2.gp120
  viruses

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Conclusion

• The results obtained from patient (HL60)
  demonstrated seroconversion deficiency, meaning
  that the patient did not produce enough
  antibodies to the increased viral load.
• But after 48 hours, during days 11, 12, and 13
  there was a reduction in viral load, thus
  indicating a relative immune response to the
  virus and potent neutralization of the infection.
  
• And there was a limited number in viral antigenic
  diversity during seroconversion.