Abstract

A group of high-molecular-weight surface-exposed proteins of nontypeable Haemophilus influenzae are major targets of human serum antibody (S. J. Barenkamp and F. F. Bodor, Pediatr. Infect. Dis. J. 9:333-337, 1990). To further characterize these proteins, we cloned and sequenced genes encoding two related high-molecular-weight proteins from a prototype nontypeable Haemophilus strain. The gene encoding a 120-kDa Haemophilus protein consisted of a 4.4-kbp open reading frame, and the gene encoding a 125-kDa protein consisted of a 4.6-kbp open reading frame. The first 1,259 bp of the two genes were identical. Thereafter, the sequences began to diverge, but overall they were 80% identical, and the derived amino acid sequences showed 70% identity. A protein sequence homology search demonstrated similarity between the derived amino acid sequences of both cloned genes and the derived amino acid sequence of the gene encoding filamentous hemagglutinin, a surface protein produced by the gram-negative pathogen Bordetella pertussis. Antiserum raised against a recombinant protein encoded by the 4.6-kbp open reading frame recognized both the 120- and the 125-kDa proteins in the prototype strain as well as antigenically related high-molecular-weight proteins in 75% of a collection of 125 epidemiologically unrelated nontypeable H. influenzae strains. The antiserum directed against the recombinant protein also recognized purified filamentous hemagglutinin. A murine monoclonal antibody to filamentous hemagglutinin recognized both the 120-kDa and the 125-kDa protein in the prototype strain as well as proteins identical to those recognized by the recombinant-protein antiserum in 35% of the nontypeable H. influenzae strain collection. Thus, we have identified and partially characterized a group of highly immunogenic surface-exposed proteins of nontypeable H. influenzae which are related to the filamentous hemagglutinin of B. pertussis.