Which immunoglobulin primarily protects secreting surfaces such as the respiratory and gastrointestinal tracts?

The correct answer is found in the function and location of immunoglobulins within the body. Immunoglobulin A (IgA) is the primary antibody that protects mucosal surfaces, such as those found in the respiratory and gastrointestinal tracts. It plays a crucial role in the immune defense by being present in secretions like saliva, tears, breast milk, and mucus.

IgA's presence in these secretions allows it to neutralize pathogens at the entry points of the body, effectively preventing infections from taking hold in these critical areas. This is particularly important in neonates and infants, where the mucosal surfaces are often the first line of defense against environmental pathogens. By being secreted onto these surfaces, IgA can bind to antigens and inhibit the adherence and entry of harmful microorganisms.

The other immunoglobulins listed have different primary functions and distribution. IgG, for instance, is the most abundant immunoglobulin in serum and provides long-term immunity and protection against pathogens in body fluids but does not primarily focus on mucosal surfaces. IgM is mainly involved in the early stages of the immune response and is present in the initial response to infection but is not specifically targeted at mucosal surfaces. IgE is associated mainly with allergic