Problem 1: Identifying Immunity Type
Question: A newborn is protected from measles for the first 6 months even without vaccination. This protection is due to which type of immunity, and what specific molecule is responsible?
Step 1: Identify the mechanism
- The newborn has NOT been vaccinated (rules out active artificial immunity)
- The newborn has NOT been infected (rules out active natural immunity)
- The protection comes from the MOTHER → this is passive immunity
Step 2: Identify natural vs artificial
- No medical intervention was involved — the transfer happened through pregnancy (biological process)
- Therefore: PASSIVE NATURAL immunity
Step 3: Identify the molecule
- Only IgG can cross the placenta (via neonatal Fc receptors on trophoblast)
- IgM (pentamer) and IgA are too large/lack the right Fc region for placental transport
- Therefore: IgG is responsible
Answer: Passive natural immunity; IgG provides protection via placental transfer