Surface-Exposed andAntigenically Conserved Determinants of OuterMembraneProteins ofBranhamella catarrhalis

Theoutermembraneproteins (OMPs)ofBranhamella catarrhalis werestudied inan effort toidentify surface-exposed determinants that are conserved among strains ofthebacterium. Aliquots ofpolyclonal antiserum were absorbed individually bystrains ofB.catarrhalis. Theabsorbed antisera were tested in comparison withunabsorbed antiserum inanimmunoblot assayagainst OMPsofthehomologous strain. The absence ofa bandrecognized byantibodies intheabsorbed antiserum compared withtheunabsorbed antiserum indicated that surface-exposed determinants oftheabsorbing strain cross-reacted withdeterminants on thehomologous strain. Twoantisera were absorbed individually by20strains ofB.catarrhalis, andthe absorbed serawerestudied inthis way inimmunoblot assays.OMP E(molecular weight, ca.56,000) expresses surface-exposed determinants that are shared among 17ofthe20strains studied. Antibodies toOMP G (molecular weight, 28,000) wereabsorbed frombothantisera by14ofthe20strains. Thesestudies demonstrate thatOMP E andOMP G expressdeterminants that areexposed on thesurface oftheintact bacterium. Furthermore, these determinants areantigenically conserved among amajority ofstrains ofB.catarrhalis. On thebasis ofthese observations, OMPsEandG should beconsidered whenbacterial antigens areevaluated as potential vaccine candidates.