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-cleaved pili from 4 strains of Moraxella bovis to react with whole or nondenatured 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 cyanogen bromide-cleaved pilin were injected into rabbits. Antisera were serially diluted, reacted with 4 strains of M bovis, and examined by immunoelectron microscopy and indirect immunofluorescence. Results - Antisera to whole pili aggregated and distorted pili from homologous strains, but pili from heterologous strains were unaffected. Antisera to cleaved pilin fragments resulted in partial aggregation and thickening of homologous and heterologous pili, suggestive of heterospecific antibodies. Attachment of antibodies to pili was detected by indirect immunofluorescence, indicating a strong reaction of antisera to whole pili with homologous pili. Weak cross-reactions were evident with certain heterologous strains. In contrast, antisera to cleaved pilin fragments reacted strongly with pili from homologous and heterologous strains. Conclusions and Clinical Relevance - We detected shared antigenic determinants on pili from various strains of M bovis that were not immunogenic in intact pili. These sites were immunogenic after cleavage of pilus protein with cyanogen bromide, and antisera produced to protein fragments reacted with whole pili from heterologous strains of the organism. Vaccines produced from cyanogen bromide-treated pili may induce broader immunity against infectious bovine keratoconjuctivitis than that provided by currently available vaccines.