Mucosal immunity induced by parenteral immunization with a live attenuated Venezuelan equine encephalitis virus vaccine candidate.

Induction of a mucosal immune response is generally thought to require introduction of an immunogen directly onto the mucosal surface. It has been observed, however, that live, attenuated mutants of the alphavirus, Venezuelan equine encephalitis virus (VEE), induce protection from virulent challenge at the respiratory mucosa even after parenteral inoculation. In this report, we propose a mechanism by which subcutaneous immunization with a molecularly cloned, attenuated double mutant of VEE is able to stimulate the production of mucosal anti-VEE IgA. Our results showed that the immunizing virus spread to, and replicated within, lymphoid tissues throughout the mouse. Several tissues known to be inductive sites of the mucosal immune system were found to be positive for the presence of VEE RNA by 48 hr postimmunization. Moreover, this mucosal lymphotropism resulted in the production of virus-specific IgA antibody detectable in vaginal secretions of immunized mice.