Rotaviruses are major etiologic agents of severe diarrheal disease in infants and young children throughout the world. Neutralizing antibodies to rotaviruses have been shown to be induced independently by two outer capsid proteins, VP7 and VP4; these antibodies are associated with resistance to illness. The baculovirus expression system has been used to successfully express the VP4 of various rotavirus strains. The protein synthesized in this system exhibits native conformation based on its reactivity with polyclonal and available monoclonal antibodies (MAbs). In addition, guinea pigs immunized with such proteins developed antibodies that neutralized infectivity of the immunizing rotavirus efficiently. Moreover, immunization of guinea pigs with the expressed VP8 or VP5 cleavage subunit of VP4 induced antibodies that also neutralized rotavirus infectivity. Results obtained by cross- immunoprecipitation and by neutralization assay with these antisera suggest that the VP8 subunit of VP4 contains the major antigenic sites responsible for the neutralization of rotavirus via VP4. A major objective of this study was to characterize the VP4 protein of the murine rotavirus Eb strain (VP7 serotype 3 and define the mucosal immune response to this outer capsid protein in the homologous mouse model. We chose as a mucosal vector the human tuberculosis vaccine, bacille Calmette- Guerin (BCG), an attenuated strain of mycobacterium bovis that has been used extensively and safely in humans. BCG vaccine is commonly given at birth and elicits a long-lasting immune response with a single dose. It is also a highly effective adjuvant.