Antibody transfer via breastmilk represents an evolutionary strategy to boost immunity in early life. Although SARS-CoV-2-specific antibodies have been observed in the breastmilk, the functional quality of these antibodies remains unclear. Here, we applied systems serology to characterize SARS-CoV-2-specific antibodies in maternal serum and breastmilk to compare the functional characteristics of antibodies in these fluids. Distinct SARS-CoV-2-specific antibody responses were observed in serum and breastmilk of lactating individuals previously infected with SARS-CoV-2, with a dominant transfer of IgA and IgM into breastmilk. Although IgG were present in breastmilk, they were functionally attenuated. We observed a preferential transfer of antibodies capable of eliciting neutrophil phagocytosis and neutralization compared to other functions, pointing to selective transfer of certain functional antibodies to breastmilk. These data highlighted the preferential transfer of SARS-CoV-2-specific IgA and IgM to breastmilk, accompanied by select IgG subpopulations, positioned to create a non-pathologic, but protective barrier against COVID-19 disease.
Selective functional antibody transfer into the breastmilk after SARS-CoV-2 infection