Diseases and Immunity: Question 4
Syllabus 10.1
A foal (baby horse) is born prematurely and fails to suckle enough of its mother's first milk (colostrum) in the hours after birth. Because of this, a veterinarian injects the foal with a solution containing ready-made antibodies against tetanus, extracted from the blood of another, already-immune horse.
Which statement correctly describes the type of immunity the foal gains from this injection, and whether memory cells are produced as a result?
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Worked solution
Step 1: Identify who made the antibodies
The foal did not make these antibodies itself. They were extracted from the blood of another, already-immune horse, then injected into the foal. Immunity gained from antibodies made by another individual, rather than by the individual’s own body, is passive immunity.
Step 2: Recall whether memory cells form in passive immunity
Memory cells are only produced when an individual’s own lymphocytes are stimulated to respond to antigens, as happens during active immunity, for example after an infection or a vaccination. Because the foal’s own immune system was never stimulated to make these particular antibodies, no memory cells are produced in the foal, and the protection this injection gives is short-term.
Step 3: Rule out the other options
- A and B (active immunity): incorrect, because the antibodies came from another horse’s blood, not from the foal’s own body.
- C (passive immunity; memory cells produced): correctly identifies passive immunity, but passive immunity never involves memory cell production.
Final answer
- The foal gains passive immunity, and no memory cells are produced, option D.