Why is IgA protected from digestion in the intestine?

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Diagram of an antibody molecule showing two identical light chains and two identical heavy chains joined by disulfide bonds in a Y-shaped structure, with labeled regions for antigen binding and effector function. — antibody The four-chain structure of an antibody, or immunoglobulin, molecule. The basic unit is composed of two identical light (L) chains and two identical heavy (H) chains, which are held together by disulfide bonds to form a flexible Y shape. Each chain is composed of a variable (V) region and a constant (C) region.

IgA is protected from digestion in the intestine because it is secreted into the intestinal lumen as "secretory IgA," which is complexed with a specific glycoprotein produced by the epithelial cells of the mucosa.1

When this substance attaches to the IgA molecule, it shields the antibody from being broken down by protein-splitting enzymes present in the digestive tract. This structural adaptation allows the antibody to remain functional, enabling it to adhere to viruses and bacteria, interfere with their growth, and neutralize toxic substances within the intestine.1