The polymeric immunoglobulin receptor, PIGR, of 764 aas and 2 TMSs, one N-terminal and one at residue 650, near the C-terminus, contains two repeats (residues 31 - 128 and 361 - 455). It mediates selective transcytosis of polymeric IgA and IgM across mucosal epithelial cells. It binds polymeric IgA and IgM at the basolateral surfaces of epithelial cells. The complex is then transported across the cell to be secreted at the apical surface. During this process, a cleavage occurs that separates the extracellular (known as the secretory component) from the transmembrane segment. Through its N-linked glycans, it ensures anchoring of secretory IgA (sIgA) molecules to mucus lining the epithelial surface to neutralize extracellular pathogens (Phalipon et al. 2002). On its own (free form) it may act as a non-specific microbial scavenger to prevent pathogen interactions with epithelial cells (Perrier et al. 2006). The regulatory functions of secretory immunoglobulins (i.e., sIgA) after transport across the membrane by pIgR in Bactrian camel (Camelus bactrianus) lungs (He et al. 2022).