Isotype-specific antibody responses to rotavirus and virus proteins in cows inoculated with subunit vaccines composed of recombinant SA11 rotavirus core-like particles (CLP) or virus-like particles (VLP).

The isotype antibody responses to bovine IND P5, G6 and simian SA11 P2, G3 rotavirus and SA11 rotavirus proteins (VP4, VP6 and VP7) in serum, colostrum and milk were analysed by ELISA in three groups of vaccinated cows and nonvaccinated controls. Pregnant cows were vaccinated intramuscularly and intramammarily with recombinant baculovirus-expressed SA11 rotavirus VLP (triple-layered virus-like particles containing rotavirus VP2, VP4, VP6 and VP7); CLP (double-layered core-like particles containing rotavirus VP2 and VP6); or inactivated SA11 rotavirus, respectively. Rotavirus antigen titers were highest (30-200-fold) in ELISA in the VLP vaccine compared to the inactivated SA11 vaccine. The IgG1, IgG2 and IgM geometric mean antibody titers (GMT) to rotavirus (titers to bovine rotavirus vs SA11 rotavirus did not differ significantly for any isotype or group) and the IgG2 GMT to VP6 in serum at calving in the vaccinated groups were significantly (P < 0.05) higher than in the control group. In colostrum, IgG1 and IgA rotavirus antibody titers were significantly elevated for VLP (IgG1 GMT 832225; IgA GMT 16384), CLP (IgG1 GMT 660561; IgA GMT 10321) and SA11 (IgG1 GMT 131072; IgA GMT 1448) vaccinated cows compared to control cows (IgG1 GMT 11585; IgA GMT 45). The IgG1 and IgA GMT to rotavirus were significantly elevated (6-100-fold) in milk of VLP and CLP vaccinated cows compared to SA11 vaccinated or control cows. The isotype antibody responses to VP6 in serum, colostrum and milk paralleled the responses to rotavirus, but titers were approximately 2-10-fold lower. Only cows vaccinated with VLP had significantly enhanced serum, colostral and milk antibody titers to rotavirus VP4 and VP7. These results demonstrate that rotavirus antibody titers in serum, colostrum and milk are significantly enhanced by use of non-infectious VLP, CLP and inactivated SA11 rotavirus vaccines, but the VLP or CLP vaccines induced the highest antibody responses, corresponding to their higher rotavirus antigen titers measured by ELISA.