Practice question

Agglutination requires cross-linking of particulate antigens such as erythrocytes or bacteria into clumps visible macroscopically. IgM is pentameric comprising five immunoglobulin monomers joined by J chain, presenting ten antigen-binding sites arranged in star-like plane. This multivalency provides high avidity and spans greater intercellular distance, efficiently bridging cells despite electrostatic repulsion and zeta potential. IgG is bivalent and smaller, less capable of overcoming repulsive forces without enhancement media. IgE and IgA have other effector roles. Clinically, anti-ABO isohemagglutinins are often IgM, explaining potent blood group agglutination.