Isotype conversion of Staphylococcal-specific IgG into IgM broadens the reactivity to other bacterial pathogens

A new study in Cell Reports Medicine shows that converting highly specific anti-Staphylococcus IgG antibodies into the IgM isotype can dramatically broaden their ability to bind and protect against other bacterial pathogens. The researchers found that the IgM versions, due to their pentameric and multivalent structure, gained cross-reactivity to several Gram-positive and Gram-negative bacteria—including E. coli and Neisseria meningitidis—and even conferred in vivo protection against Streptococcus pyogenes infection. This isotype conversion not only altered the antibody’s Fc functions but also changed the Fab-antigen interactions, thereby expanding binding specificity. The findings open a new avenue for designing broad-spectrum antibody-based therapies against resistant bacteria, offering a promising complementary strategy to antibiotics in tackling antimicrobial resistance.