An infant's introduction to the world of germs begins at birth, when the baby is exposed to maternal and environmental bacteria during delivery (a vaginal birth immediately seeds the baby with bacteria; a caesarian delivery delays this natural process, but only for a few days). This initial contact with a hostile environment teeming with microbes and other foreign substances turns out to be a good thing. It sets into motion a series of responses that help prime the baby's immune system.

Our immune system is designed to react to anything foreign. When a pathogen enters the infant's body, a system of special cells mobilizes in a coordinated defense response. This can involve the secretion of specific molecules to bind to and neutralize the pathogen, or it can involve special cells that engulf or otherwise eliminate the germ.

The immune system is a balancing act, and the balancing act is even trickier for a baby whose immune system is still developing. Imagine a biological game of friend or foe, in which the right password must be given to get inside the clubhouse. As the guardian of the clubhouse, the immune system must protect against foreign threats, such as disease-causing bacteria or viruses. Yet it must also be able to tolerate other foreign particles, like proteins in food or harmless microbes. You don't want your baby's immune system to underreact and not guard against harmful bacteria, but you also don't want it to over-react to harmless substances in the infant's diet or environment.

When it comes to the immune system, there are two facts that many people don't know. First, the gastrointestinal tract is the largest immunological organ in the body; along with tissue dedicated to digestion and absorption of nutrients, the intestine also contains immune tissue known as gut-associated lymphoid tissue (referred to as GALT). And second, there are far more beneficial microbes within the GI tract than we might imagine.

Beneficial Bacteria
Healthy adults have about 3 pounds of bacteria living on and in their bodies. The microbes you carry along with you actually outnumber your human cells 10 to 1. Scientists have long known there are many mutually beneficial relationships between animals and microbes that have evolved over millions of years. We give the microbes a place to live in our digestive systems and these microbes, in turn, provide benefits to us. Some researchers have referred to our intestinal microbiota as a virtual "organ within an organ." Here's why:

Beneficial microbes increase the surface area of the intestinal lining by stimulating the growth and development of special fingerlike projections in the gut lining called villi. The microbiota also stimulate the growth of specialized cells in the immune system.

Beneficial microbes can break down complex substances into simpler compounds, and in the process make available otherwise inaccessible nutrients. They even produce necessary nutrients, such as vitamin K, which is important for blood clotting. (It takes about 6 weeks for the newborn to produce adequate amounts of the vitamin, and because of this delay, babies are typically given a vitamin K shot at birth.) At the same time, beneficial microbiota also change the chemistry of the gut in ways that can discourage the growth of pathogens.

Beneficial microbes such as Bifidobacterium and Lactobacillus can inhibit the ability of pathogens to attach themselves to the gut lining and also outcompete pathogens for nutrients. This keeps the population of pathogens low and creates a natural barrier against attack and colonization by pathogens. And this, in turn, lowers the risk of intestinal infection and disease. By maintaining an intestinal barrier, beneficial microbes help prevent germs from crossing the intestinal wall and entering the bloodstream.

Nutrition also plays an important role in helping the baby's immune system mature. Colostrum is rich in immune factors, including antibodies, which lend the baby temporary, or passive, immunity. Mature breast milk continues to provide the baby with many important immune factors, though their concentration decreases. There are also indigestible components in breast milk that promote the healthy development of beneficial intestinal flora. Called human milk oligosaccharides (HMOs) or prebiotics (in formula), these compounds provide food to beneficial bacteria. The fermentation of the HMOs by gut bacteria makes the pH of the gut more acidic, which helps maintain an environment unsuitable for the proliferation of pathogenic bacteria.

Innate and Adaptive Immunity
The immune system is comprised of two systems working together: the innate immune system and the adaptive immune system. Each system uses different specialized cells to carry out its defense.

Innate immunity is the line of defense that responds to infection, wounds, or pathogens in a nonspecific, or generic, manner, meaning that all foreign cells are treated the same. This type of immune response is more primitive, in evolutionary terms, and relies on a range of white blood cells, or leukocytes, that seek out and destroy foreign cells, or strive to isolate and protect damaged tissue through defensive measures such as inflammation. Innate immunity is a blank slate and remains unchanged no matter how often it encounters a particular foreign cell.

Adaptive immunity, on the other hand, is a line of defense that "learns" and forms cellular "memories" about the exact identity of each invader. This enables the system to prepare for future encounters with a specific invader and mount even more effective countermeasures. Adaptive immunity relies on antibodies that circulate in the body and serve as the immunological memory that offers long-lasting protection against specific pathogens. Vaccines are possible because of the adaptive immune system.

Nutrition is important for both innate and adaptive immune systems. Studies have found that vitamins such as A, C, B6, B12, E, and folate as well as minerals such as iron, selenium, and zinc along with certain fatty acids all play important roles in the health and development of the immune system. Protein is also important, and a deficiency in this nutrient can result in poor wound healing, impaired tissue repair, and reduced resistance to infection.



More on this topic

Infant Nutrition (VIDEO)
Fueling Growth & Development
Milk Enters the Stomach
Milk Enters the Small Intestine
Some Key Nutrients
Gut & Immune Development
Respiratory Health
Skeletal & Muscular Development
Skin & Hair Growth
Cardiovascular Development
The Importance of Fat
DHA & ARA
Nervous System Development
Good Nutrition Builds Healthy Babies


Related Health Centers:

Infant Nutrition Health Center, Mother-Baby Bond Health Center, Mother’s Milk Health Center, Monthly Infant Development Calendar Health Center,Weekly Pregnancy Calendar Health Center