Identification ofAnaplasma marginaleOuter Membrane Protein Antigens Conserved betweenA. marginaleSensu Stricto Strains and the LiveA. marginalesubsp.centraleVaccine

Abstract

Live vaccination withAnaplasma marginalesubsp.centrale(synonym forAnaplasma centrale) induces protection against severe disease upon challenge withA. marginalesensu stricto strains. Despite over a century of field use, the targets of protective immunity remained unknown. Using a broad proteomic approach, we identified the proteins in a challenge sensu stricto strain that were bound by the relevant antibody isotype induced by live vaccination withAnaplasma marginalesubsp.centrale.A core of 15 proteins was identified in vaccinated animals across multiple major histocompatibility complex (MHC) haplotypes. This core separated into two structural/functional classes: “housekeeping” proteins involved in replication and metabolism and outer membrane proteins (OMPs). Orthologous proteins of both classes were identified within the vaccine strain and among sensu stricto strains. In contrast to the broad conservation among strains in the sequences of the housekeeping proteins, there was significantly greater divergence in the OMPs and greater divergence in both OMP sequences and the encoding locus structure between the vaccine strain and the sensu stricto strains than among the sensu stricto strains. The OMPs bound by live vaccine-induced antibody overlapped with OMPs that were immunogenic in animals vaccinated with inactivated vaccines and subsequently protected against bacteremia and disease. The identification of this core set of OMPs is consistent with the hypothesis that “subdominant” immunogens are required for vaccine-induced protection againstA. marginaleand provides clear direction for development of a safer, more effective vaccine.

Primary Structural Variation in Anaplasma marginale Msp2 Efficiently Generates Immune Escape Variants

“…Collectively, 89% of the expressed structural variants were also antigenic variants across all replicates, independent of a specific MHC haplotype. The biological relevance of these findings is supported by the following four lines of evidence: (i) all structural variants were expressed during infection of a natural host, (ii) the structural variation observed in the microdomains corresponded to the mean length of variants generated by segmental gene conversion in the St. Maries strain (29 Ϯ 13 nucleotides, based on examination of 1,183 variants [9]), (iii) antigenic variants were identified using a broad antibody response that developed during infection of a natural host, and (iv) the ablation of antibody binding to a variant microdomain is in agreement with the results demonstrating lack of binding to a newly emergent full-length HVR (22,23).…”

Identification of a T-Cell Epitope That Is Globally Conserved among Outer Membrane Proteins (OMPs) OMP7, OMP8, and OMP9 of Anaplasma marginale Strains and with OMP7 from the A. marginale subsp. centrale Vaccine Strain

“…marginale OMPs 7 to 9 are promising vaccine candidates because they are recognized by IgG2 and T cells from cattle immunized with the protective A. marginale OM fraction (7,17) and by IgG2 from cattle immunized with live A. centrale (8). The production of IgG2 generally requires the induction of CD4 T-cell help to promote isotype switching.…”

“…These proteins are considered to be logical vaccine candidate antigens because they are surface exposed, present in protective OM and cross-linked OM proteins, recognized by immune serum IgG2 and T cells in cattle immunized with the protective OM antigen preparation, and recognized by immune serum from cattle immunized with the A. centrale vaccine strain (8,(16)(17)(18). This epitope, together with additional T-cell epitopes that we have shown are present within these proteins, may be important for inclusion in a multivalent vaccine for A. marginale that can provide protection against disease caused by geographically distant bacterial strains in cattle that express common BoLA class II haplotypes DRB3*1201 and *1501.…”

“…In A. centrale, this locus is represented by one gene that encodes a protein designated OMP7, which has 64 to 70% identity with OMPs 7 to 9 of A. marginale (15). In addition, OMPs 7 to 9 are highly conserved among North American strains of A. marginale for which sequence information exists (8,14). Inclusion of conserved T-and B-cell epitopes is an important consideration for a vaccine to provide broad strain cross-protection.…”

“…centrale (here referred to as A. centrale)-immunized cattle (7,8). A. centrale is a live vaccine currently in use in many countries to protect cattle against heterologous virulent A. marginale strains (5,(9)(10)(11).…”