IMMUNOLOGICAL AND STRUCTURAL RELATIONSHIPS OF THE MINOR PILUS SUBUNITS AMONG HAEMOPHILUS-INFLUENZAE ISOLATES

Two proteins, HifD and HifE, have been identified as structural compon ents of Haemophilus influenzae pill, Both are localized at the pilus t ip, and HifE appears to mediate pilus adherence to host cells, In this study we examined the immunologic and structural diversity of these p ilus subunits among type b H, influenzae (Hib) and nontypeable H. infl uenzae (NTHI) strains. Western immunoblot analysis revealed that antib odies directed against the C terminus of HifD and HifE from Rib strain Eagan bound to HifD and HifE proteins, respectively, of all piliated Rib and NTHI strains tested. Whole-cell enzyme-linked immunosorbent as says showed that antibodies specific for native HifD or HifE of strain Eagan also bound to all piliated Rib strains but did not bind to the piliated NTHI strains. Antibodies against HifE of strain Eagan inhibit ed the binding of Rib to human erythrocytes but did not inhibit the bi nding of NTHI strains. Restriction fragment length polymorphism (RFLP) analysis was used to determine strain-to-strain structural difference s within hifD and hifE genes, either by PCR or by nucleotide sequence analysis, DNA and derived amino acid sequence analyses of HifD and Hif E confirmed the uniqueness of the RFLP types. The hifD and hifE genes of all type b strains showed identical restriction patterns. Analysis of hifD and hifE genes from the NTHI strains, however, revealed seven unique RFLP patterns, suggesting that these genes encode proteins with diverse primary structures. These results indicate that HifD and HifE are immunologically and structurally similar among the Rib strains bu t vary among the NTHI strains.