These are great questions and I'm going to
answer them together. You're right that infants
get antibodies from their mothers. Mothers and
their children are genetically different, so it is
important to keep their immune systems from
"fighting" during pregnancy. So the fetus does
not have an active immune system until some time
after it is born. The mother's immune system is
also turned down, but we still don't know the
detail of how she fights off infections without
her body attacking her unborn child.
Since the infant will need to start fighting
off infections as soon as it's born, it gets
antibodies from its mother. This is called
"passive immunity." However, these antibodies
have the mother's "ID tags," on them, so as the
baby's immune system starts working, it attacks
them. This works out fine, because the antibodies
are there when they're needed most, but after a
few months, when the baby's immune system is
working, they are destroyed. As a result,
antibodies from the mother are not passed to her
grandchildren through her daughter. They are long
gone while her child is still a baby. So a child
who was not breasting fed will not have fewer
antibodies to pass on than a child who was.
In most mammals where this has been studied,
babies get their antibodies from the special milk
that mothers make right around birth. This
special milk is called colostrums. It is full of
antibodies and other important chemicals.
Colostrums are more important in some mammals than
As you probably know, the placenta
is the thing that acts as a life support system
for the embryo or fetus before it is born. Oxygen
and nutrients are delivered from the mother and
waste products are passed to the mother for
disposal. The blood of the mother and child don't
really mix, they just come very close.
cows and horses, antibodies can't cross the
placenta. Calves and foals are much more likely to
get sick if they do not get colostrums. Farmers
keep frozen colostrums around for baby animals
that can't get it from their mothers at birth. In
humans and rats, antibodies actually cross the
placenta from mother to fetus before birth. So in
humans colostrums are less vital, but it is
If a child feeds from
several women during the first month or two of
life, it may get a bigger variety of antibodies,
especially if the women it was nursing from were
still producing colostrums and not regular breast
A veterinarian will not give a puppy
a vaccination while it still has passive immunity.
Can you explain why?
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