Question:
The immunoglobulin shown in the image is:
The immunoglobulin shown in the image is:
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A two-unit dimer carrying a J chain and a secretory piece points to one class only.
Updated On: Jun 23, 2026
- IgA
- IgG
- IgM
- IgE
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The Correct Option is A
Solution and Explanation
Step 1: The structure shows two immunoglobulin monomers joined tail-to-tail by a J chain with an extra secretory component wrapped around it. A dimer plus J chain plus secretory component is secretory IgA.
Step 2: IgA is the main antibody of mucosal immunity. In serum it is a monomer resembling IgG and makes up only 10 to 15 percent of serum immunoglobulin, but in mucous secretions it is the predominant class and exists as this dimer.
Step 3: The J chain stabilises the dimer, and the secretory component is added as the molecule is transported across the epithelial cell into the secretion. IgM is a pentamer (five units), IgG and IgE are single monomers, so only IgA fits a dimer with secretory component. Ref: Jawetz Medical Microbiology, 27e, p.138.
Step 2: IgA is the main antibody of mucosal immunity. In serum it is a monomer resembling IgG and makes up only 10 to 15 percent of serum immunoglobulin, but in mucous secretions it is the predominant class and exists as this dimer.
Step 3: The J chain stabilises the dimer, and the secretory component is added as the molecule is transported across the epithelial cell into the secretion. IgM is a pentamer (five units), IgG and IgE are single monomers, so only IgA fits a dimer with secretory component. Ref: Jawetz Medical Microbiology, 27e, p.138.
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