Question

Which type of antibody is the only one capable of crossing the human placenta?

• A. IgA
• B. IgM
• C. IgG
• D. IgE

Hint:

IgG → Only antibody crossing placenta → Provides passive immunity to fetus.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Maternal antibodies are transferred to the fetus to provide passive immunity during the early stages of life.
Step 2: Detailed Explanation:
There are five main classes of immunoglobulins: IgA, IgD, IgE, IgG, and IgM.
IgG is the most abundant antibody in human serum and is the smallest in size (monomer).
It is the only class of immunoglobulin that can cross the placenta from the mother to the fetus.
This transfer is facilitated by specific neonatal Fc receptors (FcRn) on the placenta.
IgM is a large pentamer and cannot cross.
IgA is primarily found in secretions like breast milk (colostrum) and provides immunity after birth.
Step 3: Final Answer:
The antibody capable of crossing the human placenta is IgG.