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How do maternal antibodies protect babies before their own immune systems fully mature?

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Immune stimulation by activated helper T cells — immune system Stimulation of immune response by activated helper T cells. Activated by complex interaction with molecules on the surface of a macrophage or some other antigen-presenting cell, a helper T cell proliferates into two general subtypes, T_H1 and T_H2. These in turn stimulate the complex pathways of the cell-mediated immune response and the humoral immune response, respectively.

Maternal antibodies protect infants through a process known as passive immunity, which compensates for the fact that a newborn's own immune system is not yet fully mature.12

In humans, this protection is primarily established during pregnancy through the transfer of maternal IgG antibodies across the placenta into the fetal bloodstream. This transfer occurs throughout the final two-thirds of pregnancy, providing the newborn with a temporary supply of antibodies that mirror the mother's own immunity.13

Additionally, breastfeeding offers further immunological benefits. Early milk, known as colostrum, is rich in IgA antibodies. These proteins help protect the infant's gastrointestinal tract by inhibiting the growth of harmful viruses and bacteria.13

Because these antibodies are not produced by the infant, this protection is temporary. As the child grows, maternal antibodies are diluted and broken down through normal metabolic processes. Consequently, infants eventually become more susceptible to infections as their own acquired immunity develops slowly over time.12