Question:medium
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
Count the units, then read the extras. The picture is two Y-shaped monomers linked at their bases, with a J chain and a curling secretory component. That exact build = secretory IgA.
Elimination by valency: IgM is a five-unit pentamer (also J-chain linked, but clearly bigger and circular), IgG is a lone monomer, and IgE is a monomer too. Only IgA appears as a two-unit dimer in secretions, so a dimer with a secretory piece can be nothing else.
Function pearl: IgA guards mucosal surfaces (gut, respiratory tract, tears, saliva, colostrum). The secretory component, picked up during transcytosis across the epithelium, protects the antibody from digestive enzymes once it reaches the lumen, while the J chain holds the two monomers together. Ref: Jawetz Medical Microbiology, 27e, p.138.
Elimination by valency: IgM is a five-unit pentamer (also J-chain linked, but clearly bigger and circular), IgG is a lone monomer, and IgE is a monomer too. Only IgA appears as a two-unit dimer in secretions, so a dimer with a secretory piece can be nothing else.
Function pearl: IgA guards mucosal surfaces (gut, respiratory tract, tears, saliva, colostrum). The secretory component, picked up during transcytosis across the epithelium, protects the antibody from digestive enzymes once it reaches the lumen, while the J chain holds the two monomers together. Ref: Jawetz Medical Microbiology, 27e, p.138.
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