Immune response to foot-and-mouth disease virus in an experimental murine model. II. Basis of persistent antibody reaction.

A murine model was used to study the mechanisms involved in the prolonged immune response to live and inactivated foot-and-mouth disease virus (FMDV). The antibody response elicited by the infection persisted throughout the entire life of the animal, while immunization with inactivated virus induced a transient response. The administration of inactivated virus in a water-in-oil emulsion increased antibody titres to values as high as those obtained by infection. There was a high correlation between neutralizing antibody titre and transfer of immunity with primed cells, and the protection afforded against challenge with infectious virus. It appears that the mechanism involved in the induction of prolonged immune memory in infected animals is not due to viral persistence. Nude mice infected with FMDV also evidenced a prolonged immune response, showing marked differences in antibody levels but equal effectiveness against challenge when nu/nu and nu/+ animals were compared. Furthermore, athymic and euthymic littermates were efficient in conferring protection when cells were transferred to irradiated animals. It is concluded that there is an effective, T-cell-independent, prolonged immune memory against FMDV in this murine model, and that the difference in the immune responses to live and inactivated virus is due mainly to differential antigenic processing rather than to a difference in the degree of sensitization of effector cells.