In a dimeric IgA molecule, the structure printed in red and indicated by the red arrow is called the

In a dimeric IgA molecule, the structure printed in red and indicated by the red arrow is called the

• A. J-piece
• B. Hinge region
• C. Heavy chain
• D. Light chain

Answer: (A)

The structure between the two IgA units is the joining chain, or J chain. In a dimeric IgA, two IgA monomers are linked by this small polypeptide that forms disulfide bonds with each monomer, effectively bridging them into a single dimeric molecule. It is not part of the heavy or light chains, and the hinge region is a flexible segment within a single heavy chain, not the linker between two IgA units. The J chain is essential for polymerization and also enables interaction with the polymeric Ig receptor to transport the dimer across mucosal surfaces, producing secretory IgA.

The structure between the two IgA units is the joining chain, or J chain. In a dimeric IgA, two IgA monomers are linked by this small polypeptide that forms disulfide bonds with each monomer, effectively bridging them into a single dimeric molecule. It is not part of the heavy or light chains, and the hinge region is a flexible segment within a single heavy chain, not the linker between two IgA units. The J chain is essential for polymerization and also enables interaction with the polymeric Ig receptor to transport the dimer across mucosal surfaces, producing secretory IgA.