Evaluation of IgG 2 Reactivity in Cattle Inoculated with Recombinant Outer Membrane Protein 7, 8 and 9 of Anaplasma Marginale

Abstract

Presently, there is a surge in vaccine development strategies with focus on the subunit vaccines using outer membrane proteins (OMP) which are sub-dominant surface antigens. The specific antigens that induce protective immunity against A. marginale are not known. Immunization with individual OMPs has been unsuccessful in providing protection against homologous strain challenge in the natural bovine host as compared to that achieved by immunization with OM. The current study examines if Omps serve as better immunogens for the development of cross-protective vaccine. Omp7-9 have encoded CD4+ T cell epitope that are universally conserved among geographic isolates of A. marginale. This finding has positioned OMPs 7 – 9 of A. marginale as prospective vaccine candidate. The goal of this study was to determine whether immunization of cattle with recombinant Omp (rOmp) 7 - 9 proteins will trigger IgG 2 secretions as a surrogate for adaptive immunity. The current study has demonstrated, for the first time in Ghana, > 500mg/ml of Omp 7 – 9 of A. marginale can be expressed and purified as a 45kDa recombinant protein (rOmp 7 – 9). Also, for the first time in Ghana, when administered to calves subcutaneously, rOmp 7-9 stimulated innate immune responses resulting in the development of IgG production, consistent with the induction of adaptive immune response. Firstly, experimental calves have expressed significant levels of the essential biomarkers for innate immunity. This included increased expression of IL – 6 (p < 0.05) from 100pg/ml to 1000pg/ml and of TNFα within 48 hours. Innate immune responses progressed to adaptive immunity by the significant rise in IgG 2 secretion (p= 0.02) as compared to control cohorts. This high amount of IgG 2 readout in inoculated calves compared with non - inoculated calves (p = 0.014) signifies the potential Omp 7 – 9 in inducing protective immunity and therefore a candidate for vaccine development against worldwide prevalent Anaplasma marginale. Most importantly, the IgG 2 secretions in experimental calves injected with rOmp 7 – 9 comparable to IgG 2 secretions prevailing in the population of cattle naturally infected with A. marginale (p = 0.10). Together, these results provide empirical evidence that vaccination with recombinant Omp7 - 9 would trigger the development of significant amounts of IgG Friesian x Sanga F1 crossbred calves.