Final answer:
The secreted form of IgA includes a secretory component, which is crucial for its role in immune defense by transporting IgA across mucosal membranes and protecting it from degradation, allowing it to trap pathogens in mucus.
Step-by-step explanation:
The secreted form of IgA includes a secretory component. This additional polypeptide chain enables IgA's secretion and is key to IgA's role in immune defense. The secretory component of IgA helps in the transport of the IgA dimer across mucosal membranes and stabilizes IgA against proteolytic degradation. The primary purpose of secretory IgA is to trap pathogens in mucus to prevent infection. It is vital in protecting mucosal surfaces by binding to pathogens and inhibiting their entry into the body. By doing so, secretory IgA contributes to the immune system's first line of defense, particularly in mucosal areas such as the gastrointestinal, respiratory, and genitourinary tracts, as well as in saliva, breast milk, and tears.