A baby's immune system is not fully developed until he/she is about six months-old. In the meantime, pregnant mothers pass immunoglobulin antibodies from their bloodstream, through the placenta, and to the fetus. These antibodies are an essential part of the fetus's immune system. They identify and bind to harmful substances, such as bacteria, viruses, and fungi that enter the body. This triggers other immune cells to destroy the foreign substance.
Immunoglobulin G (IgG) is the only antibody that crosses the placenta to the fetus during pregnancy. IgG antibodies are the smallest, but most abundant antibodies, making up 75-80% of all the antibodies in the body. They are present in all body fluids and they are considered to be the most important antibodies for fighting against bacterial and viral infections.
These antibodies help protect the fetus from developing an infection inside the womb.
Immediately after birth, the newborn has high levels of the mother's antibodies in the bloodstream. Babies who are breastfed continue to receive antibodies via breast milk. Breast milk contains all five types of antibodies, including immunoglobulin A (IgA), immunoglobulin D (IgD), immunoglobulin E (IgE), IgG, and immunoglobulin M (IgM). This is called passive immunity because the mother is "passing" her antibodies to her child. This helps prevent the baby from developing diseases and infections.
During the next several months, the antibodies passed from the mother to the infant steadily decrease. When healthy babies are about two to three months old, the immune system will start producing its own antibodies. During this time, the baby will experience the body's natural low point of antibodies in the bloodstream. This is because the maternal antibodies have decreased, and young children, who are making antibodies for the first time, produce them at a much slower rate than adults.
Once healthy babies reach six months of age, their antibodies are produced at a normal rate.
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General: During the last few weeks of pregnancy until several days after childbirth, new mothers secrete thick, yellow-white milk from their breasts called colostrum. Although colostrum is low in volume, it contains high amounts of carbohydrates (sugar), proteins, and antibodies. It is also low in fat, making it easier for newborns to digest. Colostrum acts as a laxative, helping babies pass their first stools. About seven to 10 days after delivery, the mother begins to secrete breast milk.
Research suggests that babies who are breastfed are less likely to develop infections (especially lung infections, ear infections, and diarrhea) during their first year of life than babies who are fed formulas. This is because the mother's breast milk contains important antibodies, enzymes, fats, and proteins that help boost the baby's immune system.
Although baby formulas contain all of the important vitamins and nutrients a growing baby needs, manufacturers have not been able to replicate all of the components in breast milk. Formulas lack antibodies and they are more difficult for newborns to digest.
Antibodies: Normally, acid in the stomach is strong enough to break down and destroy immunoglobulin antibodies. However, the baby's stomach acid does not break down the antibodies in the mother's breast milk. This is because the mother's mammary (breast) glands package immunoglobulins with a protective substance. This allows the immunoglobulin to reach the infant's intestine, where it is absorbed into the bloodstream. Once the immunoglobulins enter the bloodstream, they move throughout the body, searching for any foreign substances that may harm the body.
Infants who are breastfed primarily receive immunoglobulin A (IgA) via breast milk. IgA antibodies are primarily found in the nose, airway passages, digestive tract, ears, eyes, saliva, tears, and vagina. These antibodies protect body surfaces that are frequently exposed to foreign organisms and substances from outside of the body. Therefore, the mother's IgA helps the infant fend off disease-causing organisms that enter these body surfaces.
The other four types of immunoglobulin, including immunoglobulin D (IgD), immunoglobulin E (IgE), immunoglobulin G (IgG), and immunoglobulin M (IgM), are also transmitted to the baby through breast milk. These antibodies also help with immune functioning.
IgD antibodies are found in small quantities in the tissues that line the abdominal and chest cavity of the body. Even smaller amounts are present in the blood. The function of IgD antibodies is not well understood. Researchers believe that they play a role in allergic reactions to some substances, such as milk, medications, and poisons.
IgE antibodies reside in the lungs, skin, and mucous membranes. They induce allergic reactions against foreign substances, such as pollen, fungus spores, parasites, and animal dander. IgE antibody levels are often high in people who have allergies. When IgE is active, an allergic reaction occurs.
IgM antibodies are the largest type of antibody. They are found in the bloodstream and lymph fluid. The IgM antibodies are the first antibodies that are produced in response to an infection. They also stimulate other immune system cells to produce compounds that can destroy foreign invaders.
Lysozyme: An enzyme called lysozyme is also present in breast milk. This enzyme enhances the ability of IgA to fight against certain disease-causing organisms.
Oligosaccharides: Sugar molecules called oligosaccharides prevent harmful bacteria from multiplying and causing an infection. They bind with bacteria, forming a compound with the bacteria that the baby excretes from the body.
Milk lipids (fats): Milk lipids (fats) damage the outer surface of certain types of viruses. When the viruses are damaged, they are unable to replicate and cause an infection in the baby.
Proteins: A protein called lactoferrin is present in breast milk. When this protein binds to iron, it prevents disease-causing bacteria from consuming it. Bacteria need iron to survive. Therefore, lactoferrin helps kill the bacteria and infection is prevented.
Another protein called mucin is present in breast milk. Mucin attaches to bacteria and viruses that enter the baby's body. When this happens, other cells in the immune system will destroy the disease-causing substance.
Two proteins called interferon
and fibronectin also help destroy viruses that enter the baby's body.
Since babies have underdeveloped immune systems, they are more vulnerable to infections and diseases than adults, even with the passive immunity they gain through their mothers. Thus, several vaccines are given to babies to help protect them against illnesses.
Vaccines work by stimulating the body's immune system. Vaccines contain small amounts of inactivated, disease-causing organisms. This allows the immune system to produce antibodies to the foreign invader. Once antibodies are developed, the immune system is able to respond quickly to the infection if the disease-causing organism ever enters the body. After receiving a vaccine, the patient becomes immune to the specific illness.
Babies typically receive vaccines for diphtheria, tetanus, hepatitis, pertussis (whooping cough), polio, measles, rubella (German measles), mumps, and a type of flu called Hemophilus B. influenza.
Most vaccines are given when the baby reaches two months old because this is when the high level of antibodies passed on by the mother begins to decline. Many vaccines require more than one shot. These additional shots, also called booster shots, ensure that enough antibodies are produced to make the vaccine effective.
In general, vaccines are considered safe and effective for babies. Side effects may include a mild fever or skin rash.
If babies are exposed to certain types of food at a young age, they may be more likely to develop food allergies. This occurs when the child's immune system overreacts to proteins in certain foods called allergens. Allergy symptoms may range from mild to severe. The most severe reaction, called anaphylaxis can be potentially life threatening. The most dangerous symptoms are chest pain, difficulty breathing, shock, and loss of consciousness, all of which can be fatal.
Low-dose exposure to peanut protein or peanut oil products may cause peanut allergies in children, according to one study. The American Academy of Pediatrics recommends that children do not eat peanuts or peanut-containing products until they are three years old, if they have experienced allergies to other foods. Strawberries should also be avoided until the baby is about 10-12 months old.
Children whose mothers have food allergies are more likely to inherit the allergy if they are born by cesarean section (surgical delivery of the baby, also called C-section), according to one study. One study of children with allergic mothers who had C-section deliveries found that the babies were seven times more likely to develop food allergies than predisposed children who were born vaginally.