Final answer:
Secretory IgA and pentameric IgM can both bind to the poly-Ig receptor allowing their transport across mucosal surfaces. IgA is prominent in bodily fluids, providing mucosal immunity by neutralizing pathogens.
Step-by-step explanation:
Secretory IgA and pentameric IgM can bind to the poly-Ig receptor and be transported into the lumen of the gut or across other mucosal surfaces. Immunoglobulins, such as IgA, are crucial for the mucosal immune system, protecting the body's extensive mucosa. Secretory IgA, in its dimeric form, is predominantly found in bodily fluids like saliva, tears, breast milk, and mucus secretions of the gastrointestinal, respiratory, and genitourinary tracts. It operates cooperatively with IgM, which can also be secreted into these fluids. The transport across mucosal surfaces involves a polymeric immunoglobulin receptor (poly-Ig receptor), which facilitates the movement of these immunoglobulins to external secretions where they contribute to immune defense by neutralizing pathogens.