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

Abstract

Within the protective outer membrane (OM) fraction of Anaplasma marginale, several vaccine candidates have emerged, including a family of OM proteins (OMPs) 7 to 9, which share sequence identity with each other and with the single protein OMP7 in the vaccine strain A. marginale subsp. centrale. A. marginale OMPs 7 to 9 are logical vaccine candidates because they are surface exposed, present in the OM immunogen and protective cross-linked OM proteins, recognized by immune serum IgG2 and T cells in cattle immunized with OM, and recognized by immune serum IgG2 from cattle immunized with the A. centrale vaccine strain. We report the identification of a globally conserved 9-amino-acid T-cell epitope FLLVDDAI/VV shared between A. centrale vaccine strain OMP7 and the related A. marginale OMPs 7 to 9, where position 8 of the peptide can be isoleucine or valine. The epitope is conserved in American A. marginale strains, in the Australia Gypsy Plains strain, and in multiple field isolates from Ghana. This epitope, together with additional T-cell epitopes that are present within these proteins, should be considered for inclusion in a multivalent vaccine for A. marginale that can provide protection against disease caused by globally distributed bacterial strains.

Anaplasma marginale outer membrane protein vaccine candidates are conserved in North American and South African strains

“…All three OMPs had conserved N-and C-termini and the majority of the variability was found in the central regions. The recently described CD4 T-cell epitope, FLLVDDA(I/V)V (Deringer et al, 2017), was present in all of the South African Omp7, Omp8 and Omp9 sequences (Fig. 1).…”

Genomic analysis on Brazilian strains of Anaplasma marginale

“…Since the host response to membrane antigens is strictly dependent on the composition of the surface complex, it is reasonable to hypothesize that the lack/deletion of one molecule could affect the immunological response of other surface proteins. Thus, as omp9 has been considered a vaccine candidate, and it is highly recognized by immune serum of cattle immunized with outer membrane fraction; it is possible to hypothesize that changes in gene sequence (or deletions) may affect the interaction of A. marginale and host immune system (Deringer et al, 2017). Hence, further studies involving omp9 genotyping in other A. marginale strains seem to be essential for improving the epidemiological data and elucidating the roles of this gene in infection.…”

Detection and Characterisation of Anaplasma marginale and A. centrale in South Africa

“…The antibody-sensitive neutralization epitope, Q(E)ASTSS, as first described by Allred et al [ 40 ], and both T-cell (VSSQSDQASTSSQLG) [ 41 ] and B-cell (SSAGGQQQESS) [ 42 ] epitopes have been described in the N-terminal repeat region of the Msp1a protein. More recently, Omp7–9 have been reported to possess a T-cell epitope (FLLVDDAI/VV) which is conserved between the three A. marginale OMPs across strains from America, Australia and Ghana, as well as A. centrale [ 43 ]. These epitopes have not been examined in South African strains.…”