Role of macrophages in early protective immune responses induced by two vaccines against foot and mouth disease

► We studied two vaccines in their ability to achieve early protection against FMDV. ► Both vaccines yielded protection against the virus at 4 and 7 dpv in a mouse model. ► Both vaccines induced FMDV-specific, but non neutralizing, antibody titers. ► Macrophages play a central role in the response elicited by the vaccines. ► Opsonization and phagocytosis play a main role in early protection against FMDV. Foot and Mouth Disease (FMD) is an acute disease of cloven-hoofed species. We studied the protection and early immune response induced in the murine model by vaccines formulated with inactivated virus and two different adjuvants. The presence of IMS12802PR or ISA206VG adjuvants yielded protection against viral challenge at early times post vaccination and induced FMDV-specific, but non neutralizing, antibody titers. In vivo macrophage depletion in vaccinated mice severely decreased the protection levels after virus challenge, indicating a central role of this cell population in the response elicited by the vaccines. Accordingly, opsonophagocytosis of FITC-labelled virus was augmented in 802-FMDVi and 206-FMDVi vaccinated mice. These results demonstrate the ability of the studied adjuvants to enhance the protective responses of these inactivated vaccines without the increase in seroneutralizing antibodies and the main role of opsonization and phagocytosis in the early protective immune responses against FMD infection in the murine model.