Which scenario describes naturally acquired passive immunity?

Which scenario describes naturally acquired passive immunity?

• A. Antibodies pass from mother to fetus across the placenta.
• B. Antibodies produced by the recipient's own immune cells after infection.
• C. Vaccination with an antigen.
• D. Administration of antibodies to a patient.

Answer: (A)

Naturally acquired passive immunity involves receiving ready-made antibodies from someone else, rather than making your own antibodies. When antibodies pass from mother to fetus across the placenta, the newborn gains immediate protection without needing to mount its own immune response. This protection is real but temporary, since the maternal antibodies will wane as the infant’s immune system matures. The other scenarios describe different types of immunity and not this natural, passive form: antibodies produced by the recipient’s own immune cells after infection mean the person has generated their own response (active immunity). Vaccination introduces an antigen to stimulate the person’s own immune system (also active). Giving antibodies directly to a patient provides protection without the recipient making antibodies, but it is artificial rather than natural.

Naturally acquired passive immunity involves receiving ready-made antibodies from someone else, rather than making your own antibodies. When antibodies pass from mother to fetus across the placenta, the newborn gains immediate protection without needing to mount its own immune response. This protection is real but temporary, since the maternal antibodies will wane as the infant’s immune system matures.

The other scenarios describe different types of immunity and not this natural, passive form: antibodies produced by the recipient’s own immune cells after infection mean the person has generated their own response (active immunity). Vaccination introduces an antigen to stimulate the person’s own immune system (also active). Giving antibodies directly to a patient provides protection without the recipient making antibodies, but it is artificial rather than natural.