9 November 2019 | New Scientist | 15Human vision ImmunologyGege Li Debora MacKenzieIMAGINE looking across a sparkling
lake on a sunny day. Did your pupils
contract? It turns out that simply
thinking about a bright light is
enough to change the size of our
pupils, even if there isn’t anything
real for our eyes to react to.
Our pupils dilate in dark
conditions to let more light into
our eyes. The reverse happens
in bright conditions, which cause
our pupils to contract.
A team led by Nahid Zokaei at
the University of Oxford looked at
whether thinking about brightness
can be enough to alter the size
of people’s pupils. In a series of
experiments, the team repeatedly
showed 22 healthy men and
women dark or light patches,
each of which was associated
with a specific sound.After 2 seconds, the patches
disappeared. The participants
then had to picture the correct
patch in their mind when they
heard its corresponding sound.
The team found that people’s
pupils dilated when thinking of a
dark patch and contracted when
picturing a light one, the same
results that would be expected
when actually looking at the
objects (PNAS, doi.org/ddhq).
This seemingly small action
could allow us to anticipate a
change in real brightness before
it happens, says Sebastiaan
Mathôt at the University of
Groningen in the Netherlands,
who carried out a similar study
that also confirmed this finding.
For example, this reaction
could mean our pupils constrict
just before we turn on a light in
a dark room to prepare us for
the resulting glare, he says. ❚You can change the
size of your pupils
just by thinkingMEASLES is known to make
children vulnerable to other
infections. Now two studies of
Dutch Orthodox Protestants,
who reject vaccination, have
discovered why: it massively
damages the immune system,
making measles even more
lethal than we realised.
After measles vaccination
began in the 1960s, cases of the
disease plunged. Mysteriously,
wherever these vaccinations
were given, deaths from
unrelated infections also fell.
In 2015, Michael Mina, now at
Harvard University, found that
children who have had measles
are so much more likely to catch
other diseases that such post-
measles infections may account
for half of all infectious disease
deaths in children living in areas
where measles circulates.
Around 100,000 children
died of measles in 2017. Mina
suspects that two or three
times that number who
survived the disease will later
die of other infections they
wouldn’t have caught if they
hadn’t had measles.
To understand why, Mina
and his team determined whatantibodies were made by
77 unvaccinated Dutch children
who later caught measles.
As we are exposed to
pathogens as children, we
accumulate specialised
immune cells, each of which
has learned to make antibodies
to attack one particular bit of
a pathogen. The measles virus
kills these cells, but the impact
of this wasn’t known.
The team found that before
any of the children had measles,
they could make antibodies to
many viruses and bacteria. But
afterwards, they lost between
11 and 73 per cent of their
antibody library, for all kinds of
pathogens. The live, weakened
measles virus in the MMR
vaccine had no such effect in
the 32 other children studied
(Science, doi.org/ddhv).
To get their lost antibodies
back, Mina suspects those
who had measles must be
re-exposed to all the pathogens
they had already encountered,
with the attendant risks ofdisease. They may need to be
given any previous vaccinations
again too, as vaccines work by
teaching the immune system
to make specific antibodies.
It might be even worse than
that. In another study, Colin
Russell at the University of
Amsterdam in the Netherlands
and his colleagues sequenced
the DNA of immune cells from
20 of the same group of
children. “We could look not just
at cells producing antibodies,
but at their naive, precursor
cells,” says Russell.
In our first few years of life,
these naive cells mature,
diversifying so they can rapidly
recognise certain molecules on
different pathogens. Russell’s
team found that measles kills
the mature cells (Science
Immunology, doi. org/ddhw).
“It’s as if our immune system
is reset back to infancy.”
This means that those who
have had measles may need
to be re-exposed to diseases
multiple times to rebuild their
antibody repertoire, he says.
It could take five years for
their immune systems to
recover, as this is how long
it takes in people given the
powerful immunosuppressive
drug rituximab, which depletes
the same cells and is used to
treat some kinds of cancer. This
agrees with studies showing
that the immunity of people
who have had measles is
lowered for up to five years.
The effect has real clinical
impact. Russell’s team gave
a virus similar to measles to
ferrets vaccinated against flu.
When exposed to flu, these
animals went on to have bad
bouts of illness. Vaccinated
ferrets who didn’t get the
measles-like virus were still
protected against flu. ❚The long and deadly
shadow of measles
JIMWEST
/SCIENCE
PHOTO^ LIBRARYA child in Michigan
receives the
MMR vaccine“ This could mean our pupils
constrict before we turn
on a light in a dark room to
prepare us for the glare”