Researchers from the University of California found that higher concentrations of certain bioactive components known as human milk oligosaccharides (HMO) in milk were associated with protection against postnatal HIV transmission in infants.
"In developing countries, HIV-infected mothers are faced with the decision of whether or not to breastfeed their babies," Lars Bode, assistant professor in the Department of Pediatrics at San Diego School of Medicine, said.
Bode and colleagues set out to find why the vast majority of breast-fed infants do not acquire HIV-1, despite continuous exposure to the virus in their mother's milk over many months.
Even in the absences of antiretroviral drugs, only 10 to15 per cent of infants will acquire HIV infection from their HIV-infected mothers.
They discovered that immunologically active components HMO - a type of carbohydrate made up of several simple sugars linked together - may protect from HIV transmission.
These complex oligosaccharides are the third-most abundant component of breast milk, yet are not digestible and therefore become highly concentrated in the mucosal surfaces of the infant's gastrointestinal tract.
"HMO act as prebiotics that promote the growth of desirable bacterial communities in the infant's intestine," Bode said in a statement.
Additionally, HMO structurally resembles sugar chains called glycans that are normally found on epithelial cell surfaces, and can serve as "decoy" receptors to inhibit pathogens from binding.
HMO also exhibit anti-inflammatory activity and have been shown to modulate immune cell responses in cell and animal models.
The researchers analysed HMO amount and composition in breast milk samples collected from more than 200 women as part of a larger study of HIV-infected women and their infants in Lusaka, Zambia, following them from birth to 24 months.
Higher concentrations of HMO in milk were associated with protection against postnatal HIV transmission, independent of other known risk factors.
The study was published in the American Journal of Clinical Nutrition.
