International Board of Certified Lactation Consultant (IBCLC) Practice Exam

Secretory IgA is primarily localized in which tissue of the human body?

1. Blood vessels

2. Mucous membranes

3. Lymphatic system

4. Skin

The correct answer is: Mucous membranes

Secretory IgA (sIgA) is predominantly found in mucous membranes throughout the human body, making it the primary antibody present in secretions that protect mucosal tissues. These secretions include saliva, tears, breast milk, and mucosal linings of the gastrointestinal and respiratory tracts. The function of sIgA is to provide immunity at mucosal surfaces by preventing the adherence and penetration of pathogens, such as bacteria and viruses, into epithelial cells. Its presence in body secretions helps form a crucial part of the immune barrier, especially in areas exposed to external environmental threats. While blood vessels, the lymphatic system, and skin are engaged in immune responses and contain various immune components, they do not serve as the primary site for secretory IgA activity. The blood vessels carry antibodies throughout the body but do not localize sIgA specifically. The lymphatic system plays a critical role in the immune system by transporting lymph, but it is not the primary location for secretory IgA. Skin also has immunological functions and contains different antibodies and immune cells, but again, it does not specifically harbor secretory IgA as mucosal tissues do. Therefore, mucous membranes are the correct answer as the main localization of