The interaction of primate transferrins with receptors on bacteria pathogenic to humans

The binding of primate transferrins by receptors in the human pathogens Neisseria meningitidis, Moraxella (Branhamella) catarrhalis, and Haemophilus influenzae was assessed and compared with the binding of anti-human transferrin monoclonal antibodies by primate transferrins. In competitive binding assays the three pathogens showed identical specificity for primate transferrins. Only human, gorilla, chimpanzee and orangutan sera were capable of blocking binding of labelled human transferrin. Direct binding assays and affinity isolation of receptor proteins confirmed that chimpanzee transferrin, but not rhesus monkey transferrin, was capable of effectively binding to the bacterial receptors. Five distinct patterns of binding were seen when five anti-human transferrin monoclonal antibodies were reacted with the primate transferrins and these patterns reflected phylogenetic relatedness of these species to humans. A monoclonal antibody which showed transferrin-binding specificity identical to that seen with the bacterial receptors was found to block binding of human transferrin by receptors in the three bacterial species.