A large, antigenically conserved protein on the surface of moraxella catarrhalis is a target for protective antibodies

A monoclonal antibody (MAb) to Moraxella catarrhalis 035E bound to a surface-exposed epitope of a proteinaceous antigen of this organism. The antigen, designated Usp.A, was present in every strain of the pathogen tested in a colony blot RIA. UspA had amolecular mass on SDS-PAGE that varied between 300 and 400 kDa, depending on the individual M. catarrhalis strain. Passive immunization of mice with the UspA-reactive Mab enhanced pulmonary clearance of M. catarrhalis. Use ofthis Mab to screen aM. catarrhalis genomic DNA library permitted identification of a recombinant bacteriophage expressing the M. catarrhalis UspA protein. The recombinant UspA protein was used in Western blot analysis with sera from patients with M. catarrhalis pneumonia. Convalescent-phase sera but not acute-phase sera from these patients contained antibodies to this M. catarrhalis surface protein, indicating that M. catarrhalis strains growing in vivo express this molecule.