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Good bacteria, the role of breastmilk in immune system development and that "one" bottle by Lakeshore Medical Breastfeeding Medicine Clinic
In
a perfect world, a term, healthy newborn comes into the world
vaginally.
Again, I want to talk about normal. I know the process doesn't go
normally
all the time. (And I've talked about this here.)
The
delivery of that baby close to the anus is critical for immune system
development. The healthy, term newborn's gut is sterile (without
bacteria)
and the bacteria that get into that pristine gut are truly important.
During a vaginal delivery, the largely harmless bacteria around the
mother's
anus are the bacteria getting into the newborn gut. They increase in
number, compete for food and space and help coordinate efforts to create
a
healthy gut for that baby. With the exception of our skin, the gut is
the
largest immune system organ in our body.
Because breastfeeding is normal, what happens to healthy, term newborns
who are
breastfed is normal. The newborn has a delay in their immune response
to
bacteria. A delay? To a bacteria? Yup. Normal.
After delivery, that newborn gut has many challenges from invaders that
may not
be friendly. Doesn't seem too smart not to fight back.
We
all have mechanisms in our body to fight infection. In the gut it's
called
Gut Associated Lymphoid Tissue (GALT) and it's ready to roll at 19 weeks
of
gestation. All of the things that make up the GALT are waiting for a
specific series of events to occur after delivery, when, if it proceeds
normally, will result in a functioning immune system.
The
sequence of those events is important. For example, after the good
(commensal)
bacteria has set up shop in the newborn gut, something called an
"isolated
lymphoid follicle" in the intestine of that baby develops. It's
activated
by substances in colostrum and helps with T cell development and
function.
T
cells are part of what is called the "innate" system. They mature in
the
thymus, an immune system structure found in the neck and chest of
newborns.
Human milk activates resting thymus cells, helping to shape the immune
function
of these cells. Breastfed kids have a larger thymus than those that are
not breastfed; the thymus of the breastfed child is up to twice the size
of a
child not breastfed. The innate immune system contains cells that kill
bacteria but they do it by also causing inflammation and tissue damage.
The
innate immune system is different from the "adaptive" immune system,
which is
very specific to certain invaders. (Never being very good at
immunology,
but being really great at American football, I see the innate system as
the
offensive line, generally protecting from guys coming at the
quarterback.
The adaptive immune system is more like the wide receiver or cornerback-
a
player with a more specific job)
The
cells of the adaptive immune system, antibodies, come in several
flavors: Immunoglobulin M (IgM), which is the first type of antibody
produced
and isn't very specific; IgG which is transferred across the placenta
and is the
only immunoglobulin that the baby gets from mom and has at birth (the
newborn,
with only IgG is essentially immuno-compromised); IgE which isn't too
relevant
here; and IgA which rocks. IgA is a "sticky" immunoglobulin that
protects
surface areas from infection. A special type of IgA, secretory IgA, is
found in huge numbers in human milk and protects the airway, gut and
other
mucous membranes from infection. Secretory IgA is special because the
"secretory" part is an addition to the IgA and importantly, is
resistant to being broken down by the baby' stomach and GI tract.
So,
we have a new baby, exposed immediately to bacteria...why no
inflammation?
Well, the activity of the T-cells is delayed for about 10
days (remember,
T-cells cause inflammation and tissue damage.) Well... secretory IgA
helps.
It's made by mom in response to infections in her environment and passed
to the
baby through breastfeeding. Moms and babies should stay together.
This is one good reason: mom can't make antibodies to things that the
baby is
exposed to if the baby isn't with her.
Human milk also contains special sugars, oligosaccharides, which help
feed good
bacteria. In fact, they are necessary for that good bacteria to grow.
Plus, they are a type of prebiotic-
something can block bad bacteria before they ever get to the surface of
the gut.
They let the probiotics,
the
good bacteria, stay in the gut. And because they never let the bad
bacteria get to the gut surface, no innate immune system is needed, and
we get
no inflammation or tissue damage. Oligosaccharides also work with
certain
receptors (called Toll Like Receptors). These receptors work in the
first
5 days (when are our kids getting supplemented?) and are controlled
tightly,
like hour by hour.
In
the time that the immune system is delayed, oligosaccharides, toll like
receptors and good bacteria protect against bad bacteria and avoid the
need for
an inflammatory response. Any alteration
in human milk or addition of formula interferes with toll like
receptor
function, changes the bacteria that the baby's gut gets exposed to and
can then
lead to inflammation and
tissue
damage, the result we were trying so hard to avoid.
Just one bottle.
The
lesson? Let's make sure we know why we are supplementing.
Jenny Thomas, MD, IBCLC, FAAP, FABM
More info? A very nice book from Dr. Lars Hanson on Breastfeeding and
Human Milk.
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