Question

Half life of IgG is usually

• A. 6 days
• B. 23 days
• C. 5 days
• D. 2 days

Hint:

The long half-life of IgG (23 days) makes it the most effective antibody for long-term passive immunity and is the primary reason why maternal antibodies persist in newborns for several weeks.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Immunoglobulins (antibodies) are specialized glycoproteins produced by plasma cells. Different classes of immunoglobulins (IgG, IgM, IgA, IgE, IgD) have different biological half-lives in the systemic circulation.

Step 2: Detailed Explanation:
Immunoglobulin G (IgG) is the most abundant antibody class in the blood and extravascular fluid.
It has the longest biological half-life among all the immunoglobulin classes, which is typically around 20 to 24 days (classically cited as 23 days in standard immunological literature).
This prolonged half-life is due to its interaction with the neonatal Fc receptor (FcRn), which protects IgG from intracellular lysosomal degradation and recycles it back into the circulation.
In contrast, other immunoglobulins like IgM and IgA have much shorter half-lives of approximately 5 to 6 days, and IgE has a half-life of only 2 to 3 days.
Therefore, the half-life of IgG is usually 23 days.

Step 3: Final Answer
The correct option is (B).