Fig. 1: Breastmilk as a natural way of vaccinaton.

Besides providing important but rapidly weaning passive immunity, breastmilk may actively provoke a long-lasting immune response by the transfer of low doses of microbial antigens in an infant-tailored vehicle. Breastmilk contains microbial antigens as a whole or (partially) pre-digested, presented by milk antigen-presenting cells or captured in extracellular vesicles or immune complexes. These antigens are delivered to the infant mucosa in conjunction with milk bioactive molecules and milk microbiota that can function as infant-tailored adjuvants. This may allow breastmilk to activate the neonatal immune system to induce protective, long-lasting immunity against pathogens. Image created with BioRender.