IMMUNIZATION WITH BABESIA-BIGEMINA RHOPTRY-ASSOCIATED PROTEIN-1 INDUCES A TYPE-1 CYTOKINE RESPONSE

Rhoptry-associated protein-1 (RAP-1) homologues of Babesia bigemina an d Babesia bovis are promising candidates for inclusion in subunit vacc ines against these hemoprotozoan parasites, Partial protection against challenge infection has been achieved with native forms of these anti gens, but the mechanism of immunity has not been thoroughly defined, W e previously demonstrated that a panel of antigen-specific T helper ce ll clones derived from B. bigemina RAP-1-immunized cattle expressed re latively high levels of interferon-gamma (IFN-gamma) protein and trans cript and low levels of interleukin-4 (IL-4), indicative of a type 1 i mmune response, In the current study we present evidence that subcutan eous immunization with native B. bigemina RAP-1 protein in RIBI adjuva nt 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 resti mulation of draining lymph node lymphocytes with specific antigen resu lted in proliferation and enhanced expression of IL-2 and IFN-gamma, w hereas IL-4 and IL-10 transcript levels remained relatively low, These findings show that our previously described cytokine profiles of anti gen-specific cloned T cell lines are representative of autologous in v ivo responses and confirm that type 1 recall responses to B. bigemina RAP-1 can be evoked in immunized animals by native parasite antigen.