What is the primary function of IgA in the body?

Immunoglobulin A (IgA) is primarily known for its role in mucosal immunity, which is a crucial aspect of the immune system that protects mucosal surfaces such as those in the gastrointestinal, respiratory, and urogenital tracts. By being predominantly found in secretions like saliva, tears, and breast milk, IgA functions as a key line of defense against pathogens that enter the body through these routes. This is especially important for protecting against food-borne pathogens, as IgA can neutralize these invaders and prevent infection in the digestive system.

The other choices relate to functions that do not involve IgA. Blood clotting is primarily mediated by platelets and various clotting factors, whereas cell-mediated immunity is more related to T cells and their processes. Facilitating oxygen transport is a function of hemoglobin in red blood cells, not immunoglobulins. Thus, the role of IgA in protecting against food-borne pathogens distinctly emphasizes its importance in maintaining mucosal health and overall immune defense.