Polymorphism of the major surface epitope of the CopB outer membrane protein of Moraxella catarrhalis.

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.

Phase-variation of the truncated lipo-oligosaccharide of Neisseria meningitidis NMB phosphoglucomutase isogenic mutant NMB-R6.

The detection of antibodies specific to meningococcal lipo-oligosaccharides (LOSs; outer-core-->inner-core-->lipid A) in sera of patients convalescent from meningococcal infection suggests the potential use of LOS as a vaccine to combat pathogenic Neisseria spp. Removal of the outer-core region, which expresses glycans homologous to human blood-group antigens, is a required first-step in order to avoid undesirable immunological reactions following vaccination. To this end, we describe here the structural makeup of the LOS produced by serogroup B N. meningitidis NMB isogenic phosphoglucomutase (Pgm) mutant (NMB-R6). The dominant LOS types produced by NMB-R6 expressed a deep-truncated inner-core region, GlcNAc-(1-->2)-LDHepII-(1-->3)-LDHepI-(1-->5)-[Kdo-2-->4]-Kdo-->lipid A, with one PEA unit attached at either O-6 or O-7 of LDHepII, or with two simultaneously PEA moieties attached at O-3 and O-6 or O-3 and O-7 of the same unit. Unexpectedly, this mutation did not completely deactivate the production of Glc, as some LOS molecules were observed to carry Glc at O-4 of LDHepI and at O-3 of LDHepII. A glycoconjugate vaccine comprised of NMB-R6 LOSs is currently being evaluated in our laboratory.