Protective Effect of Vaccination with Toxoplasma Lysate Antigen and CpG as an Adjuvant against Toxoplasma gondii in Susceptible C57BL/6 Mice

Abstract : Infection with the intracellular protozoan parasite Toxoplasma gondii causes serious publichealth problems to both humans and livestock and of great economic impact worldwide. Oligodeoxynu-cleotides (ODN) which contain immunostimulatory CG motifs (CpG ODN) can promote Th1 responses, anadjuvant activity that is desirable for vaccination against intracellular pathogens. We investigated thefeasibility of using CpG as an adjuvant combined with Toxoplasma lysate antigen (TLA) as a vaccineagainst toxoplasmosis. Genetically susceptible C57BL/6 mice were vaccinated with TLA with or withoutCpG ODN as an adjuvant and then challenged with 85 cysts of the moderately virulent RRA (Beverley)strain of T. gondii . Prior to challenge infection, immunization with TLA plus CpG ODN directed cellularand humoral immunity toward a Th1 pattern, characterized by enhanced INF production by splenic cellsin response to TLA, and enhanced production of toxoplasma-specific IgG and IgG 2a antibodies. Conse-quently, CpG/TLA-treated mice showed prolonged survival and 64% reduction in brain parasite burdencompared to non-CpG/TLA treated group. Our results suggest that CpG ODN would provide a stable andeffective adjuvant for use in vaccination against toxoplasmosis.