|Scientists Discover How Nipah Virus
Working independently, two research teams funded by
the National Institute of Allergy and Infectious Diseases
(NIAID), part of the National Institutes of Health (NIH),
have identified how Nipah and Hendra viruses, closely
related viruses first identified in the mid-1990s, gain
entry into human and animal cells.
Nipah and Hendra are emerging viruses that cause serious
respiratory and neurological disease. People can get
these deadly viruses from animals. Beginning in 1994,
public health officials have recognized disease outbreaks
in Malaysia, Singapore, Bangladesh and Australia.
Both viruses use a protein essential to embryonic development
to enter cells and begin their often-fatal attack, report
researchers at the University of California, Los Angeles
(UCLA) and the Uniformed Services University of the
Health Sciences (USUHS) in Bethesda, Maryland.
The UCLA team, headed by Benhur Lee, M.D., describes
its findings in a Nature paper posted online on July
6. The report by the USUHS researchers, led by Christopher
Broder, Ph.D., is appearing online the week of July
4 in the Proceedings of the National Academy of Sciences.
The first reported outbreak of Nipah virus occurred
in 1998-1999 in Malaysia, sickening 265 people and killing
105, according to the World Health Organization. This
outbreak, which in this case spread from pigs to humans,
was contained by culling more than a million pigs. Hendra
virus, so far less of a threat to human health, was
first identified in 1994 in Australia when it spread
from horses to humans.
“In addition to our concern about Nipah and Hendra
viruses as emerging global health and economic threats,
we worry about their potential use as bioterror agents,” says
Anthony S. Fauci, M.D., director of NIAID. “This work,
funded through our biodefense research program, is a
major step towards developing countermeasures to prevent
and treat Nipah and Hendra infection.”
Using different methods, both teams identified a specific
cell surface receptor, Ephrin-B2, as the doorway used
by Nipah and Hendra viruses to get inside cells. This
receptor is found on cells in the central nervous system
and those lining blood vessels. It is crucial for the
normal development of the nervous system and the growth
of blood vessels in human and other animal embryos.
Ephrin-B2 is found in humans, horses, pigs, bats and
other mammals, which explains the unusually broad range
of species susceptible to Nipah and Hendra virus infection.
Dr. Broder and his colleagues collaborated with researchers
at the National Cancer Institute, also part of the NIH,
and the Australian Animal Health Laboratory. The team
narrowed the search for the Nipah/Hendra receptor by
first sifting through the genetic sequences of 55,000
possible receptors using microarray technology as a
The scientists compared microarray signals from the
55,000 genetic sequences in one set of Nipah virus-resistant
human cells with microarray signals from three sets
of human cells that the virus can infect. This enabled
the research team to narrow the possible number of receptor
proteins to 120 by identifying those present in the
virus-susceptible cells but absent in the virus-resistant
cells. They winnowed the possibilities further — to just
21 — by selecting only those candidate receptors within
the molecular weight range they expected. They selected
10 expressed at high levels in the susceptible cell
lines and inserted them, one by one, into the cells
that resisted Nipah virus to identify the receptor.
When they inserted the gene for Ephrin-B2, the previously
Nipah-resistant cells admitted the virus.
The UCLA team, with collaborators at the University
of Pennsylvania, took a different approach, using tools
of advanced molecular biology as well as old-fashioned
detective work to identify the Ephrin-B2 receptor. They
knew the receptor would be abundant among the type of
cells Nipah virus attacks, that is, nerve cells and
cells lining blood vessels.
To identify the human cell receptor, they created
a bait: the Nipah protein that docks to that unknown
receptor was attached to part of a human antibody, like
a worm on a fishing hook. When they placed this bait
onto cells susceptible to Nipah virus infection, it
attached to a protein on the cell surface. When placed
on Nipah-resistant cells, however, the antibody did
not attach to the cells. The scientists used an instrument
that sorts molecules by weight to identify that Ephrin-B2
was the cell receptor protein that bound to the antibody/Nipah
protein “fishing pole” they had made.
They wanted to confirm their findings, but since they
did not have access to a high-level biosafety laboratory
as Dr. Broder’s team did, the UCLA researchers engineered
a harmless virus with Nipah virus proteins embedded
in its coat. The UCLA team found that this artificial
construct could infect cells vulnerable to Nipah virus
but was unable to infect Nipah virus-resistant cells.
They also showed that this engineered virus could infect
nerve cells and cells lining blood vessels using Ephrin-B2
as the receptor, in the same way as actual Nipah virus
would infect these cells.
Knowing the identity of the Nipah and Hendra receptor
will not only help in developing vaccines and treatments,
but also promises to lead to better understanding of
how the viruses cause disease in people and a variety
of animals, the researchers say.
NIAID is a component of the National Institutes
of Health, an agency of the U.S. Department of Health
and Human Services. NIAID supports basic and applied
research to prevent, diagnose and treat infectious
diseases such as HIV/AIDS and other sexually transmitted
infections, influenza, tuberculosis, malaria and illness
from potential agents of bioterrorism. NIAID also
supports research on transplantation and immune-related
illnesses, including autoimmune disorders, asthma
News releases, fact sheets and other NIAID-related
materials are available on the NIAID Web site at http://www.niaid.nih.gov.
The National Institutes of Health (NIH) The
Nation's Medical Research Agency is comprised
of 27 Institutes and Centers and is a component of the
U. S. Department of Health and Human Services. It is the
primary Federal agency for conducting and supporting basic,
clinical, and translational medical research, and investigates
the causes, treatments, and cures for both common and
rare diseases. For more information about NIH and its
programs, visit www.nih.gov.
References: MI Bonaparte et al. Ephrin-B2 ligand
is a functional receptor for Hendra virus and Nipah
virus. Proceedings of the National Academy of Sciences
vol 102 (2005) doi:10.1073/pnas/0504887102.
OA Negrete et al. Ephrin B2 is the entry receptor for
Nipah virus, an emergent deadly paramyxovirus. Nature
(2005) doi: 10.1038/nature03838.