Final answer:
Human infants receive passive immunity from their mothers through the transfer of IgG antibodies via the placenta and IgA through breast milk, protecting them early in life. The option (B) is correct.
Step-by-step explanation:
Maternal antibodies are transferred to infants, providing them with passive immunity against infections to which the mother has immunity. This transfer occurs mainly through a structure called the placenta as early as 16 weeks gestation.
IgG antibodies, in particular, can cross the placental barrier, and they protect the fetus and the newborn for the first few months after birth. Additionally, secretory IgA antibodies are also passed from mother to infant through breast milk, contributing to the immunity of the child. Therefore, option (B) is correct.
This question is not complete, Here I am attaching the complete question:
Human infants are born with a supply of maternal immunoglobulin antibody. In this way they acquire resistance to all infections to which the mother had antibody-mediated immunity. Maternal antibody is transferred as early as 16 weeks' gestation mainly via what structure?
(A) Spleen
(B) Placenta
(C) Thymus
(D) Peyer's patches
(E) Bone marrow