What facilitates the crossing and secretion of antibodies from the lamina proporia to the gut lumen

What facilitates the crossing and secretion of antibodies from the lamina proporia to the gut lumen?

The correct answer and explanation is:

The correct answer is polymeric immunoglobulin receptor (pIgR).

Explanation:

The polymeric immunoglobulin receptor (pIgR) plays a crucial role in facilitating the crossing and secretion of antibodies, specifically IgA, from the lamina propria (a layer of connective tissue in the mucosa) to the gut lumen. IgA is the primary antibody found in mucosal secretions, including those in the intestines, respiratory system, and urogenital tract.

In the process of antibody secretion, B cells in the lamina propria produce IgA antibodies. These antibodies are then transported across the epithelial cells lining the gut by the pIgR, which is located on the basolateral surface of the epithelial cells. The process involves several steps:

1. Binding of IgA to pIgR: The polymeric immunoglobulin receptor binds to the dimeric form of IgA (often referred to as IgA2) in the lamina propria.
2. Transcytosis: Once bound, the IgA-pIgR complex undergoes transcytosis, which is the process by which the complex is transported across the epithelial cell from the basolateral side to the apical surface, which faces the gut lumen.
3. Secretion into the lumen: Upon reaching the apical surface, the complex is cleaved, and the secretory component of pIgR is released along with the IgA antibody into the gut lumen. This secretory IgA (sIgA) is now active and able to function in immune defense.
4. Role of secretory IgA: Once secreted into the gut lumen, secretory IgA helps protect the mucosal surfaces by neutralizing pathogens, preventing their adherence to the epithelial cells, and enhancing immune surveillance. This process is essential for mucosal immunity, as it provides the first line of defense against ingested pathogens, toxins, and other harmful microorganisms.

In summary, pIgR facilitates the movement of IgA antibodies from the lamina propria to the gut lumen, where they serve a vital role in immune protection and the maintenance of gut health.