Passive immunity involves antibody molecules that are transferred to the baby from the mother’s active immune system through the placenta.
During prenatal development, maternal IgG antibodies are transferred from about gestational week 13 from maternal blood across the placenta.
Placenta syncytiotrophoblast cell endosomes bind IgG, in maternal blood lacunae, through neonatal Fc receptors.1
Immunoglobulin (Ig) G is the single antibody type that binds to a neonatal Fc receptor and is endocytosed via pinocytosis.
During early postnatal development, maternal IgA, IgM, IgG antibodies are transferred from breast milk into the infant gastrointestinal tract.
They provide initial protection against pathogenic microorganisms.
Passive immunity is considered to be a short-term system, which is taken over in the first year or two of life by the adaptive immune system.