Nontypeable Haemophilus influenzae (NTHI) is the causative agent of a number of acute and chronic infections, such as otitis media (OM), chronic obstructive pulmonary disease (COPD) and community-acquired pneumonia. Incidence of invasive infections such as meningitis and septicemia caused by NTHi are increasing. There is currently no vaccine against NTHi. We have previously demonstrated that Hia expression is phase-variable, with expression changes commensurate with changes in the length of a promoter located poly-T tract. The host receptor for the Hia protein is currently unknown, although we have shown that high levels of Hia expression (Hia ON) are required for host colonization. We hypothesized that host glycans may act as receptors for Hia-mediated adherence to host nasopharygeal epithelial cells; we therefore examined the glycan-binding ability of Hia using glycan arrays and Surface Plasmon Resonance (SPR).
Glycan array and SPR results show that Hia binds preferentially to sialyated glycans, with highest binding to a 2-6 sialyl-lactosamine with a KD of 237nM. This glycan is found in the human airway, and is a receptor for other human pathogens, such as Influenzae A virus. Promoter:lacZ fusions demonstrate that elements up- and down-stream of the poly-T tract must be aligned in order to achieve high level Hia expression.
Hia is highly immunogenic and has been investigated as an NTHi vaccine candidate for a number of years; our demonstration of a requirement for Hia for host colonization therefore makes it an attractive vaccine candidate despite being phase-variably expressed. Blocking host colonization by NTHi may result in lowered carriage rates, and decrease the incidence of NTHi disease. Knowledge of the host structures bound by Hia, and the method by which Hia is expressed will aid in the development of a functional blocking NTHi vaccine.