When I picked my husband up from work the other day he said he thought he might be getting sick. “My coworker has been coughing all week. He sounded terrible.” I hoped for the best — we often don’t get sick when we’ve had a known exposure, and do seemingly out of nowhere. But by that night my husband huddled under a mound of blankets, his throat sore and his body achey.
My son and I likely had a few days before the virus came for us. We were lucky to have gone the six months of his life illness-free, not needing to use the special thermometer we bought or the intimidating snot sucker. I knew that antibodies were passed in breastmilk — I remembered reading something about baby’s saliva causing antibody production in the mother, which were then transferred back to the baby. It sounded like a magical system, one that is told to new mothers with the intention of empowerment but rang overly simplified to be true. How did antibody production and transference actually work? Would my exposure to my husband’s illness keep him from getting sick? Would this happen even if I avoided the illness myself, my mounting antibodies keeping both of us well? I didn’t know.
I pulled my face close to the bright screen of my laptop, reading the research while my son napped next to me. Before babies are born, antibodies are passed from the placenta to the fetus, providing protection from infections the mother has been exposed to. But this protection doesn’t last. The half-life of these antibodies is about 21 days, which means my six month old likely had almost none of this placental protection left.1 His own immune system remained undeveloped, and his ability to protect himself remained minimal. My son was in a vulnerable position.
To fill in the immunological gap, babies ingest antibodies from breastmilk. The majority are secretory IgA antibodies that coat the surfaces of mucosal cells they come into contact with. Functioning almost like a sticky fly trap, these molecules catch viral particles before they can enter cells and cause more trouble, and are then washed away.2 Others are called IgG antibodies. These serve as backup for pathogens that get past the secretory IgA barrier, tagging them for destruction by the baby’s immune cells.3
But how does the mother’s immune system know how to make these antibodies? I learned that the saliva-based mechanism was not exactly right. This idea has some supporting evidence, but hasn’t been conclusively demonstrated in humans.45 What has been demonstrated, through decades of research, is a different mechanism called the entero-mammary pathway. When the mother’s immune system encounters a pathogen in the gut or respiratory tract, it generates IgA-producing immune cells. In a non-lactating person, these antibodies go to where the infection is. But in someone that is lactating, the mammary glands broadcast a chemical homing signal that attracts these IgA-producing cells to the breast, where the antibodies are secreted directly into the milk.67 This intricate system translates to real health protections. One study found that breastfed infants aged 0–6 months had roughly one-third fewer infections than formula-fed babies.8
All of this was happening in my body when the illness eventually came for both of us. I was the sickest I had been in awhile. My body felt like a hard shell around me, and I had a hard time mustering the energy to move and care for him. His little body burned with fever, too, but somehow was still in good spirits. He didn’t appear to develop the other symptoms I had — congestion, cough, sore throat. Why was this the case?
Two things likely protected him. As my son drank breastmilk and it coated his mouth, his esophagus, and his stomach, he was receiving protection from my antibodies. But another factor, paradoxically, was his underdeveloped immune system itself. I’ve encountered many respiratory infections in my life (unfortunately). My body sees an infection and responds in the way it knows how — lots of inflammation, an aggressive response to fight the infection. His body does not do that yet.9 This immune system naivety, in combination with the protection from my antibodies blocking some of the viral particles that were present, is likely why he was rolling around on the bed laughing while I was leaning over the edge of it, coughing up nasty chunks of phlegm.
Being able to feed my baby from my body already felt like a miracle before knowing all of this. But now, each time I nursed it felt like I was feeding him an elixir, a mix of food and medicine created from the deep knowledge of my body, made just for him.