Secretory IgA

Definition

Secretory IgA (sIgA) is an antibody that plays a crucial role in the immune defense of mucosal surfaces, such as those in the gastrointestinal, respiratory, and urogenital tracts. It is produced by plasma cells in mucosal-associated lymphoid tissue (MALT) and is unique because it exists in a dimeric form, allowing it to effectively neutralize pathogens and prevent their adherence to epithelial cells.

5 Must Know Facts For Your Next Test

1. Secretory IgA is the most abundant antibody found in mucosal secretions, such as saliva, tears, and breast milk.
2. It plays a key role in the first line of defense against pathogens by preventing their attachment and entry into epithelial cells.
3. Secretory IgA can neutralize toxins and viruses, making it vital for protecting mucosal surfaces from infections.
4. This antibody is transported across epithelial cells through a specific receptor known as the polymeric immunoglobulin receptor (pIgR).
5. In breastfeeding, secretory IgA is transferred to infants, providing them with passive immunity and helping to establish their gut microbiota.

Review Questions

• How does secretory IgA contribute to the immune defense at mucosal surfaces?
  • Secretory IgA contributes to immune defense at mucosal surfaces by binding to pathogens and toxins, preventing their adherence to epithelial cells. This action effectively blocks potential infections before they can penetrate the mucosal barrier. By neutralizing viruses and bacteria in secretions like saliva and mucus, sIgA serves as a critical first line of defense in various mucosal areas.
• Discuss the process of how secretory IgA is produced and transported to mucosal surfaces.
  • Secretory IgA is produced by plasma cells located in mucosal-associated lymphoid tissue (MALT). Once produced, it binds to the polymeric immunoglobulin receptor (pIgR) on the basolateral side of epithelial cells. This receptor-mediated transport allows sIgA to be transcytosed across the epithelial layer and released into mucosal secretions in its secretory form. The process ensures that high concentrations of sIgA are present at mucosal surfaces for effective immune protection.
• Evaluate the significance of secretory IgA in early life and its role in establishing gut immunity.
  • In early life, secretory IgA is crucial as it is transferred from mother to infant through breast milk, providing passive immunity during the first months. This transfer helps protect infants from infections while their own immune systems are still developing. Moreover, sIgA plays a role in shaping the gut microbiota by selectively binding to certain bacteria, which influences the establishment of a balanced microbiome. This early exposure helps educate the infant's immune system and promotes healthy immune responses later in life.

Related terms

Mucosal-associated lymphoid tissue (MALT): A collection of lymphoid tissues found in mucosal areas that play a significant role in the immune response, including the production of secretory IgA.

Immunoglobulin: A class of proteins that function as antibodies, with various types like IgG, IgA, IgM, IgD, and IgE serving different roles in immune responses.

Plasma cells: Specialized B cells that produce and secrete large amounts of antibodies, including secretory IgA, to combat infections.