Elisabet O. Orville
Our bodies are constantly being bombarded by viruses, bacteria and fungi, many of which live happily on our skin. It has been estimated that a normal adult male has approximately 2.41 million bacteria per cm
2
in his armpit (Marples, 1969). We stay healthy, however because we have a system of immunity that destroys most of the germs that penetrate our bodies.
When bacteria, for instance, enter the bloodstream they are recognized as foreign matter (antigens) by special white blood cells called lymphocytes which then divide repeatedly to form plasma cells. These plasma cells produce and release into the blood stream great quantities of protein molecules called antibodies, which are specific in their action against that antigen. The antibodies may cover the antigen by attaching to it or damage it in other ways. Other lymphocytes produce memory cells which are programmed against future invasions of that particular antigen.
The of antibodies that are of most importance to the fetus/newborn are IgG, IgM and IgA. (Ig stands for immunoglobulin.) They have different shapes and functions:
|
name
|
shape
|
function
|
|
|
|
Found in blood serum and
|
|
IgG
|
|
can cross placenta. Pro-
|
|
|
|
tects fetus and newborn.
|
|
|
|
Found in blood serum.
|
|
IgM
|
|
Destroys microorganisms.
|
|
|
|
Does not cross placenta.
|
|
|
|
Found in intestines, milk,
|
|
IgA
|
|
tears lining of nose.
|
|
|
|
throat and lungs. Keeps
|
|
|
|
germs from entering body.
|
(Figure available in print form)
The unborn baby lives in an almost germfree state inside the womb with the placenta as guardian against foreign attacks. At first the fetus does not make its own antibodies but is sent IgG by its mother. These different IgG antibodies are a collection of responses of the mother’s body to all the microorganisms to which she has been exposed. IgG is the only group of antibodies that can cross the placenta.
Meanwhile the fetus starts to produce IgM in its spleen and bone marrow after the tenth week and the level slowly rises to birth. (IgM does not cross the placenta.) If the neonate has very high levels of IgM in its blood at birth it is suspected that it had an intrauterine infection.
At birth as the baby moves through the vagina it starts to pick up the first of the billions of microorganisms that will be with it through life. How is it protected? First of all many of its white blood cells (leukocytes) are able to engulf these germs. Also it still has a high level of IgG which was passed to it from its mother and in addition, it can make its own IgG and IgM now.
The newborn is very vulnerable to intestinal infections, though, because it has almost no IgA which would protect it. If a new mother nurses her baby she produces colostrum, a yellowish liquid, for the first few days after birth. Colostrum contains lots of IgA as does the milk which follows. A breastfed baby has less diarrhea than a bottlefed baby (Meyer and Dwyer, 1980).
The baby also passes its germs by bodily contact to the mother who makes specific antibodies against them and returns them in the milk. Thus the nursing baby and mother continue to form the same close unit that they did prenatally with the mother providing immunologic protect— ion until the baby’s immature antibody system develops.
