Interaction of Haemophilus influenzae with human erythrocytes and oropharyngeal epithelial cells is mediated by a common fimbrial epitope.

The role of fimbriae in the adherence of Haemophilus influenzae to oropharyngeal epithelial cells and the hemagglutination (HA) of human Anton-positive erythrocytes was examined. HA of bacteria was lost after shearing. Fimbriae purified from the extracellular fluid caused HA and bound to oropharyngeal epithelial cells, as analyzed with immunoperoxidase staining, in a way which was similar to the adherence of bacteria to these cells: binding was over the entire surface of the cells and showed cell-to-cell variation. The specific role of fimbriae in HA and adherence was further examined by inhibition experiments with monoclonal antibodies elicited against the isolated fimbriae. These monoclonal antibodies bound along the entire length of the fimbriae, as seen by immunogold electron microscopy. The monoclonal antibodies and their Fab fragments inhibited HA (reduction in titer from 1:512 to 1:128 and 1:64, respectively) and inhibited the adherence of the homologous H. influenzae strain and of three of eight heterologous H. influenzae strains to oropharyngeal epithelial cells. These results indicate that fimbriae are involved in adherence and HA and that the binding site for the monoclonal antibodies on the fimbriae is not common on all strains.