**7.1 Poly immunoglobulin receptor (pIgR)**

The transfer of IgA from the production site in the mucosal and glandular tissue areas to the secretions takes place in an active process with the involvement of membrane polymer receptors (**Figure 5**).

The pIgR receptor is a membrane glycoprotein consisting of five Ig-like domains (reinforced with disulfide bounds) at the cell surface, an intramembrane fragment, and a 100-amino acid sequence within the cytoplasm.

The human immunoglobulin polymer receptor gene is located on chromosome 1. The genes of these receptors in epithelial cells are affected by cytokines such as IFN-γ in vitro and are expressed on the surface of these cells. Therefore, it can be said that mucosal inflammation has an aggravating role in the transfer of slgA to secretions [1, 66].

#### **Figure 5.**

*Mechanism of IgA dimer production in lamina propria and its transmission by epithelial cells. Lamina propria plasma cells produce IgA dimers (A). These antibodies are transported into the epithelial cells via pIgR at the basal surface (B). Following the release of IgA from the luminal surface of these cells by the mechanism of transcytosis (C), due to proteolytic cleavage, part of the receptor remains attached to the IgA dimer, which is the secretory component or SC (D).*

#### **7.2 Binding of IgA to the immunoglobulin receptor**

IgA binds to the first Immunoglobulin-like domain of the Poly-Ig receptor. Following the separation of pIgR from the epithelial cell, a disulfide bond is established between the cysteine of the fifth SC region and the Fc portion of one of the IgA monomer monomers. Domains 2, 3, and 4 of the secretory component do not participate in the binding but are necessary for the establishment of the two cysteine roots [66].
