Probing the potential interactions between two protein vaccine candidates from Nontypeable Haemophilus influenzae.

Nontypeable Haemophilus influenzae (NTHi) is the leading cause of AOM (acute otitis media) among children in the US, and NTHi infections contribute to the $6 billion in AOM-related medical costs each year. NTHi is also a leading cause of COPD (Chronic Obstructive Pulmonary Disease), the third leading cause of death in adults in the US, underlining the need for a vaccine to protect us against NTHi. Two well studied protein vaccine candidates from NTHi are OMP26 and Protein D. In preliminary studies, mice produced a robust antibody response to OMP26 and Protein D when injected individually. However, when both proteins were mixed in a single solution, Protein D antibody production was significantly suppressed. We hypothesized that an interaction between the proteins prevented Protein D's interaction with immune cells thus suppressing antibody production. Here, we discuss our biochemical approaches to study the potential OMP26-Protein D interaction, including native mass spectrometry. Preliminary results from those studies suggest OMP26 and Protein D do not form a complex in vitro.