Passive Immunity via Maternal Antibodies

Steps:

• Recall that passive immunity involves receiving pre-formed antibodies from another source, providing immediate but temporary protection.
• Identify that newborns receive antibodies from the mother during pregnancy.
• Confirm this transfer occurs across the placenta, protecting the baby from infections early in life.
• Eliminate options unrelated to antibody transfer.

Why A is correct:

• Passive immunity in newborns is defined as the transfer of maternal IgG antibodies across the placenta, granting short-term protection against pathogens.

Why the others are wrong:

• B: A sterile environment prevents exposure but does not confer immunity through antibodies.
• C: Lack of vaccination or exposure means no active immunity develops, but passive immunity still exists from the mother.
• D: The baby's antibody production is immature at birth; maternal diet supports health but doesn't enable fetal antibody creation.

Final answer: A