Intranasal immunization with liposome-formulated Yersinia pestis vaccine enhances mucosal immune responses

The induction of mucosal immune responses by a liposome-formulated Y. pestis vaccine (formaldehyde-killed whole cell vaccine; KWC) was evaluated. We demonstrated that intranasal immunization of mice with Y. pestis KWC vaccine, formulated with liposomes, significantly enhanced mucosal immune responses in the lung when compared to the responses induced with KWC vaccine alone. These immune responses were characterized by increased titres of specific IgA and IgG in mucosal secretions (lung and nasal washes), and an increased frequency of specific antibody-secreting cells in the lungs. In addition, antigen-specific proliferative responses and IFN-gamma-secreting cells were also significantly enhanced in the spleens of mice immunized with the KWC vaccine formulated in liposomes. Animals that were immunized intranasally with the KWC vaccine showed significant protection against an intranasal challenge with Y. pestis. These results highlight the importance of mucosal administration of vaccine antigens to stimulate immunity in the respiratory tract and demonstrate that liposome formulations can improve the effectiveness of conventional vaccines.