Antigenic heterogeneity and molecular analysis of CopB of Moraxella (Branhamella) catarrhalis

Outer membrane protein (OMP) CopB, an iron-repressible 81- kDa major OMP of Moraxella (Branhamella) catarrhalis has been a major focus of investigation. To assess CopB as a potential vaccine antigen, we elucidated the degree of antigenic and sequence heterogeneity in this protein among strains of M. catarrhalis. Two monoclonal antibodies, 1F5 and 2.9F, which bind to surface-exposed epitopes on CopB recognized 60 and 70% of the strains, respectively. The degree of sequence heterogeneity in CopB was assessed by cloning and sequencing the CopB gene from two different strains of M. catarrhalis and comparing with the published sequence. There was 92 to 96% homology between the sequences at the nucleotide level and 90 to 95% homology at the amino acid level. The variability in the protein sequence is confined mainly to three moderately variable regions. Restriction fragment length polymorphism (RFLP) analysis of the CopB genes obtained from 20 diverse strains by PCR was performed. Ninety percent of the potential restriction sites in the constant regions and 47% of the potential restriction sites in the variable regions were present in the 20 strains, indicating that the pattern of variable and constant areas in the CopB gene is a general pattern among strains of M. catarrhalis. We conclude that the CopB gent is largely conserved among strains of M. catarrhalis and contains discrete regions which show moderate heterogeneity among strains.