Final answer:
The poly Ig receptor transports immunoglobulins across the mucosal epithelium by binding to IgA and IgM, enabling their transcytosis through epithelial cells to neutralize pathogens.
Step-by-step explanation:
The correct option is D:
The receptor used for transporting immunoglobulins (Igs) across the barrier of the mucosal epithelium is the poly Ig receptor. This receptor is responsible for the transportation of IgG antibodies from the bloodstream across the epithelial cells of mucosal surfaces, such as the intestines and respiratory tract.
Within mucosal immunity, a pivotal role is played by the poly Ig receptor, which is responsible for the transcytosis of IgA and IgM from the basolateral to the apical side of epithelial cells. This receptor binds to the J-chain of IgA or IgM dimers in the mucosal lamina propria. Upon binding, the receptor-Ig complex is taken into the cell via endocytosis and transported across the cell. When the complex reaches the opposite side of the cell, the receptor is cleaved, and the Ig is released into the mucosal lumen. This process allows for the primary defense mechanism against the pathogens present in mucosal surfaces. The IgA or IgM can neutralize pathogens and toxins, effectively preventing them from invading the body through the mucosal surfaces.