The CopB outer
membrane protein has been considered a
vaccine candidate for the prevention of
infections due to Moraxella catarrhalis.
Monoclonal antibody 10F3 recognizes whole cells of about 70% of clinical isolates, suggesting that this
epitope is reasonably conserved. To determine whether CopB has other surface
epitopes, we analyzed M. catarrhalis isolates using polyclonal sera against recombinant CopB
proteins from a 10F3 positive isolate and a 10F3 negative isolate, and polyclonal sera against synthetic
peptides that contained the sequence corresponding to the 10F3
epitope region of three different isolates. Extensive cross-reactivity was observed with the anti-CopB sera towards purified recombinant CopB
proteins in Western blot and
antigen ELISA, implying that antigenic regions common to both
proteins were present. However, anti-CopB sera resembled anti-CopB
peptide sera in exhibiting similar binding specificity to whole cells, segregating M. catarrhalis isolates into four CopB groups. We subsequently cloned and sequenced the copB genes from representative isolates. The deduced CopB amino acid sequences and the degree of sequence identity also demonstrated the existence of the same four CopB groups. Each of the four groups had a unique sequence in the 10F3
epitope region and a fifth group had the
epitope deleted. The polymorphism of the major surface
epitope prompts further consideration regarding the utility of CopB as a
vaccine component as well as the design of an efficacious CopB-based
vaccine to achieve broad protection against
Moraxella infection.