The Newborn Immune System and Immunological Benefits of Breastmilk

A newborn does not yet have a mature immune system and is often unable
to mount an effective immune response. Newborns are generally
protected by the antibodies they receive through the placenta before
birth and through their mother's breastmilk after birth. These
antibodies will be the same ones that are circulating in the mother's
system, which will include antibodies to the microorganisms in the
mother's home environment and other places she frequents. Therefore,
babies generally have antibodies to the germs in their own homes.
However, many of the germs in a hospital environment are foreign to
both the mother and the baby, so the baby will not have antibodies to
protect against these germs, and the baby cannot create its own
antibodies against these new germs. This problem can be mitigated by
making sure that the baby is touched minimally by people other than
the mother and the immediate family, who share a common germ pool.

The greatest infectious danger to a newborn in the hospital is the
prevalence of bacteria that have developed resistance or complete
protection against antibiotics. Antibiotics are no longer effective
against these "superbugs", so there is no effective antibiotic
treatment for a "superbug" infection.

If a baby in the hospital develops an infection from one of these
"superbugs", nothing other than prayer can help them.

Excerpts from Textbooks

From Williams Obstetrics, 19th Edition, p. 1281

A major mechanism for inducing infection subsequent to birth is from
those caring for the infant who may be colonized with the organism or
may passively transfer it from another infected infant.

Myles Textbook for Midwives, Bennett/Brown, Twelfth Edition

Immunological adaptations, p. 508
Neonates demonstrate a marked susceptibility to infections,
particularly those gaining entry through the mucosa of the respiratory
and gastro-intestinal systems. Localisation of infection is poor,
"minor" infections having the potential to become generalised very
easily.
The baby has some immunoglobulins at birth, but the sheltered intra-
uterine existence limits the need for learned immune responses to
specific antigens. There are three main immunoglobulins, IgG, IgA and
IgM, and of these only IgG is small enough to cross the placental
barrier. It affords immunity to specific viral infections. At birth
the baby's levels of IgG are equal to or slightly higher than those of
the mother. This provides passive immunity during the first few months
of life.

IgM and IgA do not cross the placental barrier but can be manufactured
by the fetus. Levels of IgM at term are 20% those of the adult, taking
2 years to attain adult levels (elevation of IgM levels at birth are
suggestive of intra-uterine infection). This relatively low level of
IgM is thought to render the infant more susceptible to enteric
infections. IgA levels are very low and produced slowly although
secretory salivary levels attain adult values within 2 months. IgA
protects against infection of the respiratory tract, gastro-intestinal
tract and eyes.

Breast milk, and especially colostrum, provides the infant with
passive immunity in the form of lactobacillus bifidus, lactoferrin,
lysozymes and secretory IgA among others.

Properties and Components of Breast Milk, p. 523
Anti-infective factors - During the first 10 days there are more white
cells per ml than there are in blood.
Macrophages and neutrophils are amongst the most common leucocytes in
human milk and they surround and destroy harmful bacteria by their
phagocytic activity.

Secretory IgA and interferon are important anti-infective agents
produced in abundance by lymphocytes in human milk.

Immunoglobulins IgA, IgG, IgM and IgD are all found in human milk. Of
these the most important is IgA, which appears to be both synthesised
and stored in the breast. It 'paints' the intestinal epithelium and
protects the mucosal surfaces against entry of pathogenic bacteria and
enteroviruses. It affords protections against E. coli, salmonellae,
shigellae, streptococci, staphylococci, pneumococci, poliovirus and
the rotaviruses.

Lysozyme is present in breast milk in concentrations 5000 times
greater than in cow's milk. It is a well known general anti-infective
agent and its activity appears to increase during lactation.

Lactoferrin is abundant in human milk but is not present in cow's
milk. It effects the absorption of enteric iron, thus preventing
pathogenic E. coli from obtaining the iron they need for survival.

The bifidus factor in human milk promotes the growth of Gram-positive
bacilli in the gut flora, particularly Lactobacillus bifidus, which
discourages the multiplication of pathogens. Babies who are fed on
cow's milk formula have Gram-negative (potentially pathogenic) bacilli
in their gut flora.

Nurse-Midwifery, Helen Varney, Second Edition, p. 419

Immune System Changes
The neonate has an impaired ability to react to invading organisms. On
a cellular level there is a decreased ability of leukocytes to
concentrate where necessary. These leukocytes are less bactericidal
and phagocytic. At the humoral level the newborn has low or
nonexistent levels of the immunoglobulin antibodies IgM, IgE, and IgA.
The neonate is born, however, with IgG antibodies acquired from the
mother, which confer protection from some specific diseases. There is
a slow rise of immunoglobulin levels after 3 months of age to levels
of older children.

Maternity and Gynecologic Care, Bobak, Jensen, Zalar, Fourth Edition,
p. 470

Immune System
All newborns and especially preterm newborns are at high risk for
infection during the first several months of life. During this period,
infection represents one of the leading causes of morbidity and
mortality. The newborn is unable to limit the invading pathogen to the
portal of entry because of a generalized hypofunction of the
inflammatory and immune mechanisms (Medici, 1983).
Resistance to infection (immunity) includes both non-specific and
specific protective mechanisms. Medici (1983) summarizes the newborn's
defense mechanisms as follows:

The term and preterm neonate has an increased incidence of infection
for the first 4 to 6 weeks of life. This reflects the immaturity of a
number of protective systems which significantly increases the risk of
infection in this patient population. Natural barriers such as the
acidity of the stomach or the production of pepsin and trypsin which
maintain sterility of the small intestine are not fully developed
until 3 to 4 weeks. The membrane protective IgA is missing from the
respiratory and urinary tracts, and unless the newborn is breast-fed,
it is absent from the gastrointestinal tract as well. The immune
system is in great part suppressed; possibly this is a mechanism for
preventing maternal recognition of paternal antigens with subsequent
reject of the fetus. Finally, the qualitative and quantitative
response of the inflammatory factors and sluggish responses of the
phagocytic cells [leave the baby vulnerable to infection].

These web pages were originally composed by Ronnie Falcao, LM MS, in
Sept., 1997.

They have been updated as new information has become available.

Permission to link to these pages is hereby granted.

Contact Ronnie Falcao, LM MS