Hebrew University study suggests that infants actively transfer maternal IgG antibodies to the salivary glands – thus protecting the oral cavity and tuning the immune system early in life
We were all babies. And as such, we were completely helpless: we couldn't talk, walk, or even eat on our own. But there's another important thing that's less often thought about: our immune systems weren't ready yet either. In fact, babies hardly produce antibodies on their own.
“A baby is born immunologically unprepared for life,” explains Prof. Avi-Chai Hovav, head of the Laboratory for the Development and Function of the Oral Immune System at the Hebrew University of Jerusalem. “He goes from a relatively sterile environment, his mother’s womb, to a world full of bacteria. To survive the first months of life, the baby relies on antibodies that his mother passes on to him in various ways.
These antibodies reach the baby in two ways. Before birth, IgG antibodies pass from the mother's bloodstream through the placenta to the fetus' bloodstream, providing it with general protection. After birth, during breastfeeding, the baby receives additional antibodies through breast milk, mainly IgA, but also IgG, which mainly protect mucosal tissues, especially the digestive system.
What is the question? How do babies retain maternal antibodies in their mouths – even when not breastfeeding?
“Previous studies have shown that IgA antibodies obtained through breastfeeding coat the intestinal walls and protect them from bacteria,” says Prof. Hovav. “But that’s not all. These antibodies also affect the way the baby’s immune system develops, and the composition of the bacterial population in his body, the microbiota. This is one of the reasons why breastfeeding is considered healthy: it helps to finely tune the immune system. When such tuning is lacking, there is a higher tendency to develop allergies and diseases. Our study asked a slightly different question: What happens in the oral cavity? The mouth is the gateway to the body, the place where the baby first encounters bacteria. Unlike the intestine, where breast milk stays for a long time, in the mouth the milk is temporary, it is washed away quickly, and with it the antibodies. So do maternal antibodies still have a role in protecting the baby’s mouth?”
Through research in animal models, Prof. Hovav and his colleagues discovered a surprising mechanism: After birth, the baby actively transfers maternal IgG antibodies to its salivary glands, and from there to the saliva itself. These antibodies originate both from those the baby received from the mother before birth and from those obtained through breastfeeding. This creates a situation in which maternal antibodies are constantly secreted in high quantities into the oral cavity. The antibodies in the saliva protect the baby from harmful bacteria, while at the same time helping to “educate” its immune system to coexist with good and necessary bacteria. In this way, the baby is essentially imitating a process that only occurs later in life.
A baby is born immunologically unprepared for life, moving from a relatively sterile environment, its mother's womb, to a world full of bacteria.
“In adults, the salivary glands secrete antibodies that the body produces itself, to maintain oral health, and later also the health of the entire body. However, something unique happens at the beginning of life. Adult humans produce mainly IgA antibodies, while here the baby makes extensive use of the mother’s IgG antibodies. Why? Because at this stage of life, the person the baby is exposed to most is the mother, and also to her bacteria. A dropped pacifier being put back in the mouth, close contact, hugs, shared food, all of these transfer bacteria from the mother to the baby. At the same time, she also provides him with the antibodies that are exactly suitable for those bacteria. Thus, the maternal antibodies act as a kind of immune ‘gateway’ for the baby: they adjust his immune response and teach him to live in peace with bacteria that are essential for his development and functioning as an adult.”
“It is important to note that until a decade or two ago, oral health was seen as a purely local issue, one that was limited to the oral cavity itself,” adds Prof. Hovav. “The bulk of immunological research focused on other mucous membranes in the body, such as the intestines and lungs, while the mouth remained on the margins. In recent years, there has been a significant change in perception. Today, it is clear that oral health profoundly affects the overall health of the body. Many studies indicate a close connection between oral and gum diseases and diabetes, cardiovascular diseases, respiratory infections, arthritis, Alzheimer's, and pregnancy complications, due to the passage of bacteria and inflammatory factors from the mouth into the bloodstream. Therefore, it is so important to start life 'on the right foot' from an immunological perspective as well. This start lies, among other things, in the antibodies that the baby receives from its mother, and in the smart systems that exist in its body, which transport these antibodies in high quantities to the oral cavity, from the very beginning of life.
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