IV ­^¤åºK­n SAG1 and SAG2 are important surface molecules of T. gondii for the invasion of tachyzoites into host-cells. Previous studies have been demonstrated they are good candidates for development of vaccines against toxoplasmosis. Therefore, we used SAG1 and SAG2 to generate subunit vaccines and evaluated the protective capacity in BALB/c mice. Anti-idiotype IgG (aId-IgG) with the SAG2 internal image was prepared from anti-SAG2 monoclonal antibody in accordance with the network theory. Lymphocytes from mice immunized subcutaneously twice with 2, 4 or 8 µg aId-IgG showed great proliferations and secreted high level of IFN-£^, which is an important cytokines secreted by Th1 cells. After challenged subcutaneously with 1¡Ñ103 tachyzoites, the highest survival rate reached 88%. Further, SAG1 and SAG2 genes were respectively cloned and recombinant proteins rSAG1 and rSAG2 were prepared. Lymphocytes from mice immunized intraperitoneally twice with rSAG1 or rSAG2 displayed apparently Th1-associated responses, while lymphocytes from mice immunized subcutaneously twice with rSAG1 or rSAG2 did not. Mice immunized intraperitoneally twice with rSAG1 or rSAG2 had a survival rate of 64% which was higher than those mice immunized subcutaneously with rSAG1 or rSAG2. When mice immunized intraperitoneally twice with rSAG1 mixed with rSAG2, survival rate was even higher (71%). Therefore, mixed antigens induced higher protection. Subsequently, SAG1 gene was fused with SAG2 gene and a recombinant protein rSAG1/2 was expressed from the fused gene. Th1-associated responses were detected from lymphocytes of mice immunized intraperitoneally twice with 10 µg rSAG1/2. Interestingly, 80% rSAG1/2-immunized mice survived and it was extremely higher V than rSAG1- or rSAG2-immunized mice (64%). In an attempt to stimulate immune responses against T. gondii infections in the mucosal system, we chose heat-labile enterotoxin (LT) secreted from toxigenic E. coli as the stimulator. LTA2B and LTB genes were respectively cloned and then rLTA2B and rLTB were obtained. Moreover, LTA2B gene or LTB gene fused with SAG1 and SAG2 genes was performed and then recombinant proteins rLTA2B-SAG2/1 and rLTB-SAG1/2 were prepared. Subsequently, mice were immunized intranasally twice with rLTA2B-SAG2/1, rLTB-SAG1/2, rLTA2B mixed with rSAG1/2, or rLTB mixed with rSAG1/2. A strong protection (67%) was shown by the group of mice immunized intranasally with 10 µg rLTB-SAG1/2 or 4 µg rLTB mixed with 10 µg rSAG1/2. rLTB, rather than rLTA2B, will be a better candidate for stimulation the mucosal system. In summary, different survival rates caused by antigens prepared in the study may be attributed to many factors such as the treatment, the preparation and the dose of antigen. The highest survival rate is caused by aId-IgG (88%); the second is shown by rSAG1/2 (80%); the third is resulted from rSAG1mixed rSAG2 (71%). Although the survival rate raised by rLTB-SAG1/2 or rLTB mixed rSAG1/2 is slightly low (67%), these data demonstrate stimulators such as LT could induce anti-Toxoplasma immune response of the mucosal system. Antigens capable of inducing higher survival rates in mice should be worthy of further investigation for searching better vaccine candidates.

La toxoplasmose est un problème majeur de Santé Publique et notamment en médecine humaine. Le développement de vaccins est donc d’une grande priorité. L’efficacité de la stratégie vaccinale contre Toxoplasma gondii dépend de l’induction des réponses immunitaires muqueuse et systémique Th1. Les cellules dendritiques (CDs) ont un rôle essentiel dans l'orchestration de l’immunité innée et l’induction de l’immunité adaptative spécifique à Toxoplasma gondii. Dans cette étude, nous explorons une stratégie de vaccination originale qui consiste en l’administration par voie systémique et muqueuse de protéines de fusion capables de cibler l’antigène de surface SAG1 aux CDs, en utilisant un fragment d'anticorps de type scFv dirigé contre le récepteur d'endocytose DEC205. Nos résultats montrent que le ciblage de SAG1 aux DCs par le fragment scFv via la voie intranasale et sous-cutanée, réduit dramatiquement la charge parasitaire cérébrale par rapport à l’antigène non ciblé et est plus efficace que l’immunisation par la voie intranasale ou la voie sous-cutanée seule. Le ciblage des DCs potentialise la réponse immunitaire vers un profil Th1 par la production d’IFN-γ, d’IL-2, d’IgG2a sériques, tout en favorisant la production IgA muqueuses spécifiques. Parallèlement, nous avons montré qu’il était possible de conférer une reconnaissance par la protéine L à toutes les chaînes légères kappa, ce qui permettra dans l’avenir de purifier plus efficacement les antigènes ciblés par chromatographie d’affinité avec la protéine L. / Toxoplasmosis is a major public health problem and the development of a human vaccine is of high priority. Efficient vaccination against Toxoplasma gondii (T. gondii) requires both a mucosal and systemic Th1 immune response. Moreover, dendritic cells (DCs) play a critical role in orchestrating the innate immune functions and driving specific adaptive immunity to T. gondii. In this study, we explore an original vaccination strategy that combines administration via mucosal and systemic routes of fusion proteins able to target the major T. gondii surface antigen SAG1 to DCs using an antibody fragment scFv directed against DEC205 endocytic receptor. Our results show that SAG1 targeting to DCs by scFv via intranasal and subcutaneous administration improved protection against chronic T. gondii infection. A marked reduction in brain parasite burden is observed when compared with the intranasal or the subcutaneous route alone. DC targeting improved both local and systemic humoral and cellular immune responses and potentiated more specifically the Th1 response profile by more efficient production of IFN-γ, IL-2, IgG2a and nasal IgA. In parallel, we found a strategy to confer PpL recognition to all kappa chains. Therefore, affinity chromatography on protein L (PpL) matrix could be used to get easily highly purified targeted proteins.