Immune response to HIV can differ among twins

BY admin

December 09 2005 1:00 AM ET

Researchers at
the University of California, Los Angeles's AIDS Institute
report that they’ve discovered that each
person’s immune system responds to HIV in
different ways—even the immune systems of identical
twins. Writing in the December 5 edition of the
Journal of Virology, the scientists said
their findings show that the body’s defenses
against the virus are random rather than genetically
determined.

The researchers
followed the cases of male twins who were infected
shortly after their 1983 births in Los Angeles by blood
transfusions administered from the same donor at the
same time. Infected with the same strain of the virus,
the twins continue to live in the Los Angeles area and
grew up exposed to the same environmental factors. Yet
T-cell receptors (TCRs) reacted differently in each
twin, showing that the body's defense response was
random and unpredictable. TCRs play an important
role in the immune system by binding to the receptors on the
surfaces of viruses and then killing the invader. HIV
escapes this action by changing shape so that it does
not fit into those receptors.

"These boys are
as similar as two humans can be, yet we see
differences in how they fight the virus," said researcher
and UCLA professor of pediatrics Paul Krogstad in a
press release. "That's one more thing that makes it
difficult to develop a vaccine for everyone."

When a virus
invades a body, the cellular immune response targets
small parts of proteins in the virus. This targeting
mechanism itself is genetically determined, and the
twins' targeting of HIV was remarkably similar, even
17 years after infection. But their overall TCR
characteristics were highly divergent. This finding
demonstrates that the interaction between their immune
systems and the virus was random and
unpredictable--indicating that a "one size fits all" vaccine
may not be possible.

"If the goal is
to develop a vaccine, our findings suggest this may
not be so straightforward," said Otto Yang, associate
professor of infectious diseases at the David Geffen
School of Medicine at UCLA, and the study's lead
researcher, in a press release.

The UCLA
researchers say the results of their study have broader
implications, and could apply to other viruses such as
cytomegalovirus, a herpes virus that causes
opportunistic infections, and hepatitis C, the latter
being similar to HIV in both its changeable and chronic
nature. (Advocate.com)

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