Scientific American 2019-04

(Rick Simeone) #1

42 Scientific American, April 2019 Illustration by Tami Tolpa


Skin cell

Macrophage

B cell

Aedes aegypti
mosquito

Dengue virus 1 Dengue virus 2

FIRST INFECTION SECOND INFECTION

Antibody

How Antibodies May Aggravate Dengue


Four related viruses transmitted by Aedes mosqui­
toes cause dengue disease. A theory called anti body­
depen dent enhancement, postulated in the 1970s by
Scott B. Halstead, seeks to explain why a second
bout of dengue, with a different virus, is deadlier than
the first. A first infection, with, say, dengue virus 1,
prompts B cells to make antibodies that coat the
vi ruses and deliver them to white blood cells such as
macro phages, which trap and kill them. The B cells

sub sequently become quiescent, awakening after a
second infection to make the same anti bodies. But
antibodies to dengue virus 1 cannot bind well with, for
example, dengue virus 2. The anti bodies still de liver
the invaders to the macro phages but in a way that
enables them to escape destruc tion and instead com­
mandeer the macrophages. They use the sub jugated
cells’ machinery to repli cate them selves, flooding the
body with viruses. These release a pro tein that dam­
ages blood vessels, causing serious dengue disease.

On entering the body,
dengue virus often
attacks skin cells

Antibodies attach
to virus, covering
and disarming it

Virus is trapped
and destroyed

Virus escapes
cell defenses
and replicates

New copies of virus
are released

Antibodies are
unable to attach
well, leaving virus
partially bare
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