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Mother’s gut microbes may influence offspring’s immunity

A study in mice gave insight into how mother’s milk helps protect babies from harmful infections. Aliseenko / iStock / Getty Images Plus

For the first few weeks of life, a baby’s immune system isn’t well developed. However, a mother’s immune system offers some protection against harmful microbes even after birth. Antibodies shared through the placenta help protect a newborn from infections. By breastfeeding, mothers also share protective antibodies through their milk, boosting their child’s immune system. 

A research team led by Dr. Dennis Kasper of Harvard Medical School set out to understand how these antibodies—called maternal natural antibodies—may protect newborns from potentially life-threatening infections. The study, conducted in mice, was funded in part by the NIH’s National Institute of Allergy and Infectious Diseases (NIAID). Findings appeared in Nature on January 8, 2020.

The researchers investigated the role of the mother’s gut microbes in producing antibodies to protect against E. coli infection. The body is teeming with billions of microbes. Mounting evidence suggests that these microbial communities, known collectively as the microbiome, may influence health and disease.

The team bred newborn mice that lacked immune cells needed to produce antibodies. Some of the mouse pups were raised by mothers who also lacked the ability to make antibodies. Other pups were raised by mothers with normal immune systems. Any protective antibodies the pups received were transferred through breast milk.   

The scientists then exposed the mouse pups to E. coli that cause diarrheal illness. Infectious diarrhea is the second most common cause of death globally in children under age 5.  

The team found that maternal antibodies passed through breast milk were crucial for protection against E. coli infection. Pups raised by mothers with normal immune systems had 33-times fewer E. coli bacteria in their intestines and remained healthy. Most of the pups that had not received maternal antibodies became ill and died from the gut infection.    

The team found that a single species of normal gut bacteria could prompt the mother’s immune system to make a cross-reactive antibody, meaning that it provides protection against a similar pathogen—in this case, E. coli. Using fecal cultures, the researchers isolated Panteoa in the mother mouse’s gut. To demonstrate that Panteoa induced protection, the researchers immunized adult female mice with a strain of the bacteria, then infected their pups with E. coli. These pups were substantially more likely to survive E. coli infection than those born to unimmunized mothers.   

The researchers were also able to show how a type of antibody called IgG in the milk ingested by pups is transferred into their bloodstream via a specific IgG transporter. Taken together, the results provide insight into how a mother’s gut microbiome may lead to immunity in newborns.

“Our results help explain why newborns are protected from certain disease-causing microbes despite their underdeveloped immune systems and lack of prior encounters with these microbes,” Kasper says. “Moreover, they raise the possibility that mothers can confer immune protection to their offspring even to pathogens that they haven't themselves encountered in the past.”

—by Erin Bryant