AIDS Lifecycle

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AIDS Lifecycle

• Images and concept by
• The Museum of Science and Industry, Chicagoand
  The Chedd-Angier Production Company, Watertown,
  MA.

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AIDS Lifecycle Stage 1

• HIV, the virus that causes AIDS, is passed from
  one person to another through sex, sharing
  needles, or using contaminated blood products. A
  mother can also pass HIV to her new baby. The
  virus travels through the bloodstream to many
  different places in the body.

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AIDS Lifecycle Stage 2

• The immune system, which helps the body fight off
  illness, fights back in three ways with...
• ...custom-made antibodies...

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AIDS Lifecycle Stage 2

• ... macrophages which eat up all foreign
  invaders, and ...

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AIDS Lifecycle Stage 2

• killer T-cells which seek out and destroy cells
  that are already infected with the virus.

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AIDS Lifecycle Stage 3

• This defense is coordinated by these -- the
  helper T cells. But HIV has an ingenious battle
  strategy it attacks the T cells themselves,
  crippling the body's defenses.

• Infected helper T-cells (foreground)

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AIDS Lifecycle Stage 4

• Here's how it works HIV has a special shape on
  its surface which, like a piece of a jigsaw
  puzzle, fits perfectly into a shape on the T
  cell. This shape is a protein called CD4. The
  virus can now enter and infect the cell.

AIDS virus attaching to a CD4 receptor on a
helper T-cell
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AIDS Lifecycle Stage 5

• The virus's genetic information -- called RNA --
  is transcribed into a form that is identical to
  the cell's genetic information -- called DNA. The
  virus, now in the form of DNA, hides out inside
  the nucleus of the cell, escaping from the body's
  defenses.

HIV RNA being transcribed to DNA
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AIDS Lifecycle Stage 6

• After a while, HIV comes out of hiding and begins
  to reproduce.

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AIDS Lifecycle Stage 6

• The DNA is transcribed into many copies of RNA,
  which produce proteins for the new viruses.

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AIDS Lifecycle Stage 7

• The proteins are cut into usable pieces and
  packaged with the RNA.

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AIDS Lifecycle Stage 8

• The new viruses then bud from the cell. Each new
  virus may then go on to infect and destroy other
  T cells, weakening the immune systems defense.

Infected T-cell budding new viruses
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AIDS Lifecycle Stage 9

• After a lot of T cells are destroyed, the person
  is said to have AIDS. A person with AIDS will
  probably develop one or many opportunistic
  infections -- diseases that make people sick only
  when their immune systems are weakened. A person
  with AIDS will usually die of these opportunistic
  infections.

Opportunistic infections in the bloodstream of a
person with AIDS
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Stopping HIV Strategy 1

• This is a promising place to try to stop AIDS, by
  helping the immune system early on in its fight
  against HIV. One possibility is an AIDS vaccine.
  Here's how it would workAn uninfected person is
  exposed to a form of the virus which does not
  cause illness, but which does stimulate the
  body's defenses.

• The immune system is tricked into producing
  millions of killer
• T cells and antibodies custom-made to fight
  the virus.
• Some of these defenses stay in the body.

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Stopping HIV Strategy 1

• Later, if the person is infected with HIV, the
  immune system has a head start in its battle.
• But there are problems with this approach.
• Scientists have to make sure the vaccine itself
  doesn't make people ill.
• HIV is constantly changing, so the defenses
  stimulated by a vaccine might not be effective in
  fighting the actual virus.
• And if even a single virus escapes by hiding out
  inside a cell, it could go on to make thousands
  of copies of itself.
• So although this is a promising place in the life
  cycle to stop AIDS, there is still a lot of work
  to do before we have an effective vaccine.

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Stopping HIV Strategy 2

• To stop the virus here, we would have to keep it
  from ever attaching to a T cell. Let's see how
  this would work.
• This shape on the T cell is a protein called CD4.
  If a lot of artificial, decoy CD4 is given to an
  infected person, then HIV could attach to the
  decoys instead of to the T cells.

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Stopping HIV Strategy 2

• The problems here are that the decoy CD4 does not
  remain in the body very long, and it does not
  attach well to HIV circulating in the
  bloodstream. But improved decoy CD4 might
  eventually be used for an intense, short-term
  battle against a new infection.

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Stopping HIV Strategy 3

• This is an excellent place to try to stop AIDS,
  and in fact there are many drugs now in use that
  work at this step in the life cycle. Drugs that
  work at this step look like the building blocks
  used to make DNA. But they're faulty building
  blocks, so once they're used, the building
  process comes to a halt.
• And if the virus cannot turn its RNA into DNA, it
  cannot hide out in the cell, and it cannot
  reproduce. It sounds great, but there are
  problems with these drugs.

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Stopping HIV Strategy 3

• HIV is constantly changing, and eventually it is
  no longer tricked by these faulty building
  blocks. HIV becomes resistant to these drugs, and
  the life cycle continues the same as before.
  Another problem is that these drugs can damage
  non-infected cells which also need to make DNA to
  reproduce.
• This is a good place to break the life cycle, but
  it's not a cure.

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Stopping HIV Strategy 4

• There are some possibilities that may stop AIDS
  at this step in the life cycle. Scientists are
  trying to make drugs to stop the production of
  the virus's proteins. Without these proteins, the
  virus cannot survive.
• They're also working on a drug that would prevent
  the proteins being cut into usable pieces.
  Proteins in long uncut strands are useless, and
  the life cycle would be broken.

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Stopping HIV Strategy 4

• This is a promising place to break the life
  cycle, but these drugs are not a cure they would
  only slow down the replication of the virus.

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Stopping HIV Strategy 5

• This is a very late stage in the life cycle of
  HIV. But it might eventually be a last resort for
  stopping AIDS.
• Scientists are working on ways to boost an AIDS
  patient's immune system at this step, so that
  when new viruses bud from infected cells, the
  body's defenses are strengthened and ready to
  fight back. There also are many drugs now
  available to treat opportunistic infections,
  which are often the cause of death in people with
  AIDS.

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Stopping HIV Strategy 5

• This research is promising. But this late stage
  of HIV's life cycle is a very difficult place to
  stop AIDS.