Immunization with Babesia bigemina rhoptry-associated protein 1 induces a type 1 cytokine response

Rhoptry-associated protein-1 (RAP-1) homologues of Babesia bigemina and Babesia bovis are promising candidates for inclusion in subunit vaccines against these hemoprotozoan parasites. Partial protection against challenge infection has been achieved with native forms of these antigens, but the mechanism of immunity has not been thoroughly defined. We previously demonstrated that a panel of antigen-specific T helper cell clones derived from B. bigemina RAP-1-immunized cattle expressed relatively high levels of interferon-gamma (IFN-gamma) protein and transcript and low levels of interleukin-4 (IL-4), indicative of a type 1 immune response. In the current study we present evidence that subcutaneous immunization with native B. bigemina RAP-1 protein in RIBI adjuvant induces a predominant type 1 immune response in vivo, characterized by relatively high levels of IFN-gamma and IL-2 and low levels of IL-4 and IL-10 mRNA in the draining prescapular lymph node. Ex vivo restimulation of draining lymph node lymphocytes with specific antigen resulted in proliferation and enhanced expression of IL-2 and IFN-gamma, whereas IL-4 and IL-10 transcript levels remained relatively low. These findings show that our previously described cytokine profiles of antigen-specific cloned T cell lines are representative of autologous in vivo responses and confirm that type 1 recall responses to B. bigemina RAP-1 can be evoked in immunized animals by native parasite antigen.