Question: Why is IgA a preferred isotype for targeting pathogens at mucosal surfaces? Answer: IgA is the predominant antibody class found in external secretions, such as saliva, tears, and the gastrointestinal tract, where it exists primarily as a dimeric molecule linked by a J-chain. This structural adaptation makes specialized IgA antibodies and reagents indispensable for neutralizing viruses and bacteria at their point of entry. Furthermore, IgA's ability to engage the FcαRI receptor on neutrophils triggers potent phagocytosis and respiratory burst, offering a distinct mechanism of action for anti-infective and anti-tumor strategies.