Probing the Inter‐protein Interactions Between Two Leading Protein Vaccine Candidates from Nontypeable Haemophilus influenzae

Abstract

Acute otitis media (AOM) is a middle ear infection, which is the most common ailment in infants and young children. In the United States, three bacteria (commensal organisms in the nasopharynx) are the most common causes of AOM: Streptococcus pneumoniae, Moraxella catarrhalis, and nontypeable Haemophilus influenzae (NTHi). This study focuses on NTHi, which also causes chronic obstructive pulmonary disease (COPD), sinusitis, and other respiratory illnesses. OMP26 and Protein D are two leading candidates for a protein vaccine to prevent NTHi infections. Scientists have evaluated both of these NTHi proteins, with promising results. However, results from our preliminary study in mice showed that OMP26 and Protein D, when administered as a single vaccine formulation, leads to suppression of Protein D antibodies. We hypothesize that OMP26 physically interacts with Protein D, which results in the antibody suppression, but alternative mechanisms are also being explored. The aim of this work was to elucidate the inter-protein interactions between OMP26 and Protein D, with the goal of understanding how and why Protein D antibody suppression occurs in mice. To study these interactions, we have begun to employ several biochemical and biophysical methods, including co-immunoprecipitation experiments, size exclusion chromatography, and x-ray crystallography.