Abstract
The ability to elicit protective immune responses after intranasal immunization with rotavirus particles, either with or without the attenuated Escherichia coli heat-labile enterotoxin LT(R192G) as an adjuvant, was examined in the adult mouse model. BALB/c mice were administered one or two inoculations of psoralen/UV-inactivated, triple-layered (tl) or double-layered (dl) purified rotavirus particles. Four weeks after immunization, mice were challenged with the murine rotavirus strain EDIM, and the shedding of rotavirus antigen was quantified. Rotaviruses used for immunization included EDIM and heterotypic simian (RRV), bovine (WC3), and human (89-12) strains. tl EDIM stimulated both systemic and intestinal rotavirus antibody responses and complete protection with as little as one 1-microgram dose. Inclusion of LT(R192G) (10 micrograms) significantly increased rotavirus antibody responses and reduced antigen concentrations needed for full protection. Both dl EDIM and heterotypic dl and tl particles stimulated protection, but they did so less than tl EDIM at comparable concentrations, either with or without LT(R192G). When B-cell-deficient microMt mice were immunized with tl EDIM particles, protection was reduced to levels similar to those induced with dl EDIM and heterotypic particles in BALB/c mice. However, dl EDIM particles induced similar levels of protection in both mouse strains. The protection stimulated by tl or dl EDIM particles was not diminished by CD8 cell depletion prior to immunization in either strain of mice. These results indicate that tl EDIM induced immunity at least partially through responses to its outer capsid proteins, presumably by stimulation of serotype-specific neutralizing antibody. In contrast, the other particles stimulated protection primarily by an antibody-independent mechanism. Finally, depletion of CD8 cells had no effect on protection by either mechanism.