Natural immunity is developed through which mechanism in infants?

Natural immunity in infants is primarily developed through maternal transfer. This process involves the transfer of antibodies from the mother to the baby, either during pregnancy through the placenta or after birth through breastfeeding. These antibodies help to protect the infant from infections during the early months of life when their own immune system is still maturing.

Antibodies passed through the placenta provide passive immunity before birth, greatly enhancing the infant's ability to fight off infections. Additionally, breastfeeding provides colostrum, which is rich in antibodies and essential nutrients, further bolstering the infant's immune defenses.

In contrast, genetic inheritance does not directly confer immunity specific to pathogens, nor does exposure to environmental pathogens or vaccination constitute natural immunity development. Exposure to pathogens can lead to acquired immunity later in life, while vaccinations are an intentional method to stimulate the immune system without natural exposure to the disease. Thus, maternal transfer is the most direct and significant mechanism for establishing natural immunity in infants.