PHAGE ANTIBODIES OBTAINED BY COMPETITIVE SELECTION OIL COMPLEMENT-RESISTANT MORAXELLA (BRANHAMELLA) CATARRHALIS RECOGNIZE THE HIGH-MOLECULAR-WEIGHT OUTER-MEMBRANE PROTEIN

We used competitive panning to select a panel of 10 different human an tibodies from a large semisynthetic phage display library that disting uish between serum complement-resistant and complement-sensitive strai ns of the gram-negative diplococcus Moraxella (Branhamella) catarrhali s. Western blotting analyses and inhibition enzyme-linked immunosorben t assays showed that all phage antibodies were directed against the sa me or closely spaced epitopes on the target protein, which is the high -molecular-weight outer membrane protein (HMW-OMP) of M. catarrhalis. HMW-OMP was found in multiple isolates of complement-resistant but not complement-sensitive M. catarrhalis strains. Nucleotide sequence anal ysis demonstrated that the immunoglobulin heavy-and light-chain variab le-region genes encoding the 10 phage antibodies were remarkably simil ar, with a strong preference for basic amino acid residues in the heav y-chain CDR3 regions. This is the first report showing that competitiv e panning is a successful procedure to obtain phage antibodies against differentially expressed structures on phenotypically dissimilar stra ins of prokaryotic cells.