Detection of shared antigenic determinants on whole Moraxella bovis pili by use of antisera to cyanogen bromide-cleaved M bovis pilus protein

Objective-To determine the ability of antisera against cyanogen bromide-cle aved pili from 4 strains of Moraxella bovis to react with whole or nondenat ured pili. Sample Population-Antisera to 4 strains of M bovis produced by New Zealand White rabbits. Procedure-Pili from 4 strains of M bovis were collected and purified. Pilus proteins (pilin) were cleaved, using cyanogen bromide. Whole pilus and cya nogen bromide-cleaved pilin were injected into rabbits. Antisera were seria lly diluted, reacted with 4 strains of M bovis, and examined by immunoelect ron microscopy and indirect immunofluorescence. Results-Antisera to whole pili aggregated and distorted pili from homologou s strains, but pili from heterologous strains were unaffected. Antisera to cleaved pilin fragments resulted in partial aggregation and thickening of h omologous and heterologous pili, suggestive of heterospecific antibodies. A ttachment of antibodies to pili was detected by indirect immunofluorescence , indicating a strong reaction of antisera to whole pili with homologous pi li. Weak cross-reactions were evident with certain heterologous strains. In contrast, antisera to cleaved pilin fragments reacted strongly with pili f rom homologous and heterologous strains. Conclusions and Clinical Relevance-We detected shared antigenic determinant s on pili from various strains of M bovis that were not immunogenic in inta ct pili. These sites were immunogenic after cleavage of pilus protein with cyanogen bromide, and antisera produced to protein fragments reacted with w hole pili from heterologous strains of the organism. Vaccines produced from cyanogen bromide-treated pili may induce broader immunity against infectio us bovine keratoconjuctivitis than that provided by currently available vac cines.