Analysis of antigenic structure and human immune response to outer membrane protein CD of Moraxella catarrhalis

Moraxella catarrhalis is an important cause of otitis media in children and lower respiratory tract infections in adults with chronic obstructive pulm onary disease (COPD), Outer membrane protein CD (OMP CD) is a 45-kDa protei n which is a potential vaccine antigen to prevent infections caused by M. c atarrhalis. Eight monoclonal antibodies a ere used to study the antigenic s tructure of the OMP CD molecule by assaying recombinant peptides correspond ing to the sequence of the protein. This approach identified two surface-ex posed epitopes, including one near the amino terminus (amino acids 25 to 44 ) and one in the central region of the molecule (amino acids 261 to 331), A ssays with serum and sputum supernatants of adults with COPD revealed varia ble levels of antibodies to OMP CD among individuals. To determine which po rtions of the OR;IP CD molecule were recognized by human antibodies, three human serum samples were studied with six recombinant peptides which span t he sequence of OMP CD, All three sera contained immunoglobulin G antibodies which recognized exclusively the peptide corresponding to amino acids 203 to 260 by immunoblot assay. Adsorption experiments with whole bacteria esta blished that some of the human antibodies are directed at surface-exposed e pitopes on OMP CD, We conclude that OMP CD is a highly conserved molecule w hich contains at least two separate epitopes which are exposed on the bacte rial surface, While individual adults with COPD show variability in the imm une response to OMP CD, a specific region of the OMP CD molecule (amino aci ds 203 to 260) is important as a target of the human immune response.