Protective Effect against Neosporosis Induced by Intranasal Immunization with Neospora caninum Membrane Antigens Plus Carbomer-Based Adjuvant

Neospora caninum is an obligate intracellular protozoan responsible for abortion and stillbirths in cattle. We previously developed a mucosal vaccination approach using N. caninum membrane proteins and CpG adjuvant that conferred long-term protection against neosporosis in mice. Here, we have extended this approach by alternatively using the carbomer-based adjuvant Carbigen™ in the immunizing preparation. Immunized mice presented higher proportions and numbers of memory CD4(+) and CD8(+) T cells. Stimulation of spleen, lungs and liver leukocytes with parasite antigens induced a marked production of IFN-γ and IL-17A and, less markedly, IL-4. This balanced response was also evident in that both parasite-specific IgG1 and IgG2c were raised by immunization, together with specific intestinal IgA. Upon intraperitoneal infection with N. caninum, immunized mice presented lower parasitic burdens than sham-immunized controls. In the infected immunized mice, memory CD4(+) T cells predominantly expressed T-bet and RORγt, and CD8(+) T cells expressing T-bet were found increased. While spleen, lungs and liver leukocytes of both immunized and sham-immunized infected animals produced high amounts of IFN-γ, only the cells from immunized mice responded with high IL-17A production. Since in cattle both IFN-γ and IL-17A have been associated with protective mechanisms against N. caninum infection, the elicited cytokine profile obtained using Carbigen(TM) as adjuvant indicates that it could be worth exploring for bovine neosporosis vaccination.