Submitted to: Infection and Immunity
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/9/2003
Publication Date: 9/1/2003
Citation: Norimine, J., Mosqueda, J., Suarez, C.E., Palmer, G.H., Mcelwain, T.F., Mbassa, G., Brown, W.C. 2003. Stimulation of t-helper cell gamma interferon and immunoglobulin g responses specific for babesia bovis rhoptry-associated protein 1 (rap-1) or a rap-1 protein lacking in the carboxy-terminal repeat region is insufficient to provide protective immunity again virulent B. bovis challange. Infection and Immunity. 2003. 71(9):5021-5032. Interpretive Summary: Rhoptry-associated protein 1 (RAP-1) is a targeted vaccine antigen for Babesia bovis infection of cattle. The RAP-1 protein in B. bovis contains an NT region, which is widely conserved among all Babesia and a unique repeat-rich C-terminal region. We tested the hypotheses that the NT region of RAP-1 used as a vaccine in calves with interleukin-12 and RIBI adjuvant to induce a type 1 response, would result in immune responses comparable to or greater than those induced by full-length RAP-1 containing the C-terminal repeats, and whether a type 1 immune response to RAP-1 was able to induce protection against challenge. In spite of similar strong cellular (Th1) and humoral (IgG) immunological responses in all NT and RAP-1 vaccinated calves, both vaccines failed in elicit protection against challenge with virulent strain of B. bovis, thus we conclude that successful priming of calves with recombinant RAP-1 and adjuvants that elicit strong Th1 cell and IgG responses is insufficient to protect calves against virulent B. bovis challenge.
Technical Abstract: Rhoptry-associated protein 1 (RAP-1) is a targeted vaccine antigen for Babesia bovis and Babesia bigemina infections of cattle. The 60-kDa B. bovis RAP-1 is recognized by antibodies and T lymphocytes from cattle that recovered from infection and were immune to subsequent challenge. Immunization with native or recombinant protein was reported to reduce parasitemias in challenged animals. We recently reported that the NT domain of B. bovis RAP-1 contained immunodominant T-cell epitopes, whereas the repeat-rich CT domain was less immunostimulatory for T lymphocytes from cattle immune to B. bovis. The present study was therefore designed to test the hypothesis that the NT region of RAP-1, used as a vaccine with interleukin-12 and RIBI (catalog no. R-730; RIBI Immunochem Research, Inc., Hamilton, Mont. [now Corixa, Seattle, Wash.]) adjuvant to induce a type 1 response, would prime calves for antibody and T-helper cell responses comparable to or greater than those induced by full-length RAP-1 containing the C-terminal repeats. Furthermore, a type 1 immune response to RAP-1 was hypothesized to induce protection against challenge. Following four inoculations of either recombinant full-length RAP-1 or RAP-1 NT protein, RAP-1-specific immunoglobulin G (IgG) titers, T-lymphocyte proliferation, and gamma interferon production were similar. Similar numbers of NT region peptides were recognized. However, in spite of the presence of strong RAP-1-specific IgG and CD4+-T-lymphocyte responses that were recalled upon challenge, neither antigen stimulated a protective immune response. We conclude that successful priming of calves with recombinant RAP-1 and adjuvants that elicit strong Th1 cell and IgG responses is insufficient to protect calves against virulent B. bovis challenge.