Which class of immunoglobulin is the first to be produced in response to an infection?

Question

Which class of immunoglobulin is the first to be produced in response to an infection?

1. A. IgG
2. B. IgA
3. C. IgM (Correct answer)
4. D. IgE

Correct Answer

Option C — IgM

Detailed Solution & Explanation

The correct answer is IgM.

Key Points

• Immunoglobulin M (IgM) is the first class of antibody produced in response to an infection, that is, during the primary immune response.
• IgM is a large pentamer — five antibody units joined by a J chain — which gives it ten antigen-binding sites.
• This makes it highly effective at agglutination and at activating the complement system, even though its affinity for any single antigen is relatively low.
• Because of its size it remains largely confined to the bloodstream.
• It is later replaced by IgG through class switching; IgG is the most abundant immunoglobulin in serum, dominates the secondary immune response, and is the only antibody that crosses the placenta, conferring passive immunity on the foetus. IgA is the principal antibody in secretions such as saliva, tears and breast milk (colostrum); IgE mediates allergic reactions and defence against parasitic worms; and IgD functions as a receptor on B cells.

Exam Tip

• the clinical shortcut — IgM indicates recent infection, IgG indicates past infection or immunity.

प्रश्न (हिन्दी में)

संक्रमण के जवाब में बनने वाली पहली इम्युनोग्लोबुलिन की श्रेणी कौन–सी है?

1. A. IgG
2. B. IgA
3. C. IgM
4. D. IgE