Which components constitute the mucosal defense in the GI tract, including mucus and secretory IgA?

Which components constitute the mucosal defense in the GI tract, including mucus and secretory IgA?

• A. Gastric acid only
• B. Mucus layer and secretory IgA
• C. Bile salts only
• D. Salivary amylase

Answer: (B)

Mucosal defense in the GI tract relies on a mucus barrier coated over the epithelium and secretory IgA circulating in the lumen. The mucus layer serves as a physical shield that traps microbes and slows their access to the epithelial surface. Secretory IgA, produced by plasma cells in gut-associated lymphoid tissue, is transported across the epithelium by the polymeric Ig receptor and released into the lumen with a protective secretory component. In the lumen, secretory IgA neutralizes pathogens and toxins and prevents their adhesion to and invasion of epithelial cells, a process known as immune exclusion. This combination of a physical barrier plus an immune effector molecule in the mucosal surface is a central aspect of GI tract defense. Other components like gastric acid, bile salts, or salivary enzymes contribute to digestion and general barrier functions, but the specific pairing of the mucus layer with secretory IgA is what constitutes the mucosal immune defense at the surface.

Mucosal defense in the GI tract relies on a mucus barrier coated over the epithelium and secretory IgA circulating in the lumen. The mucus layer serves as a physical shield that traps microbes and slows their access to the epithelial surface. Secretory IgA, produced by plasma cells in gut-associated lymphoid tissue, is transported across the epithelium by the polymeric Ig receptor and released into the lumen with a protective secretory component. In the lumen, secretory IgA neutralizes pathogens and toxins and prevents their adhesion to and invasion of epithelial cells, a process known as immune exclusion. This combination of a physical barrier plus an immune effector molecule in the mucosal surface is a central aspect of GI tract defense. Other components like gastric acid, bile salts, or salivary enzymes contribute to digestion and general barrier functions, but the specific pairing of the mucus layer with secretory IgA is what constitutes the mucosal immune defense at the surface.