The C-Terminal Fragment of the Internal 110-Kilodalton Passenger Domain of the Hap Protein of NontypeableHaemophilus influenzaeIs a Potential Vaccine Candidate

Abstract

In this study, we immunized mice subcutaneously with recombinant proteins corresponding to the C-terminal region of Hap S from H. influenzae strains N187, P860295, and TN106 and examined the resulting immune response. Antisera against the recombinant proteins from all three strains not only recognized native Hap S purified from strain P860295 but also inhibited H. influenzae Hap-mediated adherence to Chang epithelial cells. Furthermore, when mice immunized intranasally with recombinant protein plus mutant cholera toxin CT-E29H were challenged with strain TN106, they were protected against nasopharyngeal colonization. These observations demonstrate that the C-terminal region of Hap S is capable of eliciting cross-reacting antibodies that reduce nasopharyngeal colonization, suggesting utility as a vaccine antigen for the prevention of nontypeable H. influenzae diseases.Nontypeable Haemophilus influenzae (NTHi), a nonencapsulated gram-negative bacterium, is the cause of a number of human respiratory tract diseases, such as otitis media, sinusitis, bronchitis, and pneumonia (15, 16). Otitis media is among the most common infections in young children. By 3 years of age, approximately 80% of children have had at least one episode of acute otitis media (25). Recurring bouts of otitis media may lead to significant hearing loss, which in turn may result in developmental delay. A vaccine that prevents nontypeable H. influenzae disease would provide major benefits to the health of children and the general population.The pathogenesis of H. influenzae disease begins with colonization of the nasopharynx. Subsequently, organisms spread to other sites in the respiratory tract, including the middle ear, sinuses, and lower airways (21). Based on in vitro and animal studies, a number of factors appear to influence the process of colonization. One such factor is the Hap adhesin, which promotes bacterial interaction with human respiratory epithelial cells and extracellular matrix proteins as well as mediates bacterial aggregation and microcolony formation (10,23).Hap belongs to the autotransporter family of proteins common among gram-negative pathogens (9). It is synthesized as a 155-kDa precursor protein, which consists of an N-terminal 25-amino-acid signal peptide, an internal 110-kDa passenger domain called Hap S , and a C-terminal 45-kDa outer membrane domain called Hap␤ (9). Hap S has serine protease activity and is released from the precursor protein via autoproteolysis. Of note, autoproteolysis is inhibited by secretory leukocyte protease inhibitor, which is a natural component of respiratory secretions. The Hap S domain is responsible for all the adhesive properties of Hap (10, 23). Furthermore, purified Hap S is immunogenic in mice, eliciting significant anti-Hap S antibody titers. In a mouse intranasal challenge model, animals immunized with purified Hap S from NTHi strain P860295 or N187 in the presence of mutant cholera toxin CT-E29H as an adjuvant are protected against nasopharyngeal colonization (5). These findings sug...

Genomic and antigenic characterization of monomeric autotransporters of Haemophilus parasuis: an ongoing process of reductive evolution

“…In this respect, in other bacterial models, immunization with recombinant AT-1 has led to different outcomes. Intranasal administration of the Hap passenger domain, a serine protease AT-1, reduces nasopharyngeal colonization upon Haemophilus influenzae challenge in mice (Liu et al, 2004). On the other hand, the highly conserved AasP autotransporter of Actinobacillus pleuropneumoniae did not confer protection in pigs when a denatured recombinant protein was injected intramuscularly (Oldfield et al, 2009).…”

Adhesion, Invasion, and Agglutination Mediated by Two Trimeric Autotransporters in the Human Uropathogen Proteus mirabilis

“…Here we demonstrate that the two trimeric autotransporters AipA and TaaP offer advantage to P. mirabilis in the upper and lower urinary tracts, respectively. Inclusion of autotransporters (trimeric or conventional) (49) in a multicomponent vaccine is effective in the case of pertactin (Bordetella pertussis) or the immunogenic Hap (H. influenzae), among others (28,57). Neither AipA nor TaaP appears to be immunogenic (32,34), but their incorporation in a multivalent vaccine to protect against P. mirabilis infections could prove beneficial.…”

Defining the Interaction of theTreponema pallidumAdhesin Tp0751 with Laminin

“…Multiple examples exist of bacterial adhesins that function as effective vaccine candidates, including the Hap adhesin from Haemophilus influenzae (42) and the collagen adhesin from Staphylococcus aureus (50). Peptide inhibitors have also been used to prevent adherence of selected bacteria to their attachment ligands, including the bacterial pathogens Streptococcus mutans (35) and Porphyromonas gingivalis (38) and the noscomial pathogen Pseudomonas aeruginosa (6).…”