Evaluation of the New Outer Membrane Protein A Epitope-based Vaccines for Mice Model of Acinetobacter baumannii Associated Pneumonia and Sepsis Infection

Abstract

Nosocomial infections caused by Acinetobacter baumannii (A. baumannii) are considered as a global serious problem in hospitalized patients because of emerging antibiotic resistance. Immunotherapy approaches are promising to prevent such infections. In our previous study, five antigenic epitopes of outer membrane protein A (OmpA), as the most dangerous virulence molecule in A. baumanii, were predicted in silico. In this study, the investigators evaluated some immunological aspects of the peptides.Five peptides were separately injected into C5BL/6 mice; then the cytokine production (interleukin-4 and interferon-gamma) of splenocytes and opsonophagocytic activity of immunized serum were assessed. To identify the protective function of the peptides, animal models of sepsis and pneumonia infections were actively and passively immunized with selected peptides and pooled sera of immunized mice, respectively. Then, their survival rates were compared with the non-infected controls.Based on the results, activated spleen cells in P127 peptide-immunized mice exhibited an increased level of IFN-γ compared with the other experimental groups, but not about the IL-4 concentration. The results of the opsonophagocytic assay revealed an appropriate killing the activity of produced antibodies against A. baumannii in a dose-dependent manner. Further, the survival rates of the mice under passive immunization with the immunized sera or active immunization with P127 peptide were significantly more than those in the control group. Moreover, the survival rate of the P127 peptide immunized group was considerably higher than that of the other peptide-immunized group.In conclusion, findings indicated that peptides derived from OmpA can be used as a promising tool for designing the epitope-based vaccines against infections caused by A. baumannii.