Vaccination with Recombinant Microneme Proteins Confers Protection against Experimental Toxoplasmosis in Mice

Abstract

Toxoplasmosis, a zoonotic disease caused by Toxoplasma gondii, is an important public health problem and veterinary concern. Although there is no vaccine for human toxoplasmosis, many attempts have been made to develop one. Promising vaccine candidates utilize proteins, or their genes, from microneme organelle of T. gondii that are involved in the initial stages of host cell invasion by the parasite. In the present study, we used different recombinant microneme proteins (TgMIC1, TgMIC4, or TgMIC6) or combinations of these proteins (TgMIC1-4 and TgMIC1-4-6) to evaluate the immune response and protection against experimental toxoplasmosis in C57BL/6 mice. Vaccination with recombinant TgMIC1, TgMIC4, or TgMIC6 alone conferred partial protection, as demonstrated by reduced brain cyst burden and mortality rates after challenge. Immunization with TgMIC1-4 or TgMIC1-4-6 vaccines provided the most effective protection, since 70% and 80% of mice, respectively, survived to the acute phase of infection. In addition, these vaccinated mice, in comparison to non-vaccinated ones, showed reduced parasite burden by 59% and 68%, respectively. The protective effect was related to the cellular and humoral immune responses induced by vaccination and included the release of Th1 cytokines IFN-γ and IL-12, antigen-stimulated spleen cell proliferation, and production of antigen-specific serum antibodies. Our results demonstrate that microneme proteins are potential vaccines against T. gondii, since their inoculation prevents or decreases the deleterious effects of the infection.

The Impact of the Antigenic Composition of Chimeric Proteins on Their Immunoprotective Activity against Chronic Toxoplasmosis in Mice

“…The SMM composition proved the least potent in preventing tissue cyst formation, although SAG1 and MAG1 recombinant proteins of similar length, and accompanied by GRA1 in a mixture, decreased tissue cyst formation in mice by 89% in previous studies [22]. Thus, the most likely explanation is that the exchange of one antigen and its length significantly influenced the resulting protective activity of the chimeric protein, although the MIC1 antigen appeared highly promising due to the results obtained by other research teams [29,30]. It is also important to remember that, to a certain degree, chimeric antigens represent an artificial product constructed experimentally, which may influence their folding and conformational stability and in turn impact immunogenicity and immune polarization [31].…”

The lectin-specific activity ofToxoplasma gondiimicroneme proteins 1 and 4 binds Toll-like receptor 2 and 4 N-glycans to regulate innate immune priming

“…This results in IL-12 secretion and the production of IFN-γ, a pivotal cytokine that mediates parasite clearance and the development of a protective T cell response [19, 22], but in some cases, as seen during RH infection of CD-1 mice, promotes a dysregulated cytokine storm and acute mortality, as seen during RH infection of CD-1 mice [36]. This MIC-TLR activation event explains, at least in part, the resistance conferred by rMIC1 and rMIC4 administration against experimental toxoplasmosis [20, 21].…”

“…For the recombinant proteins, rMIC1 and rMIC4 sequences were amplified from cDNA of the T. gondii strain ME49 with a 6-histidine tag added on the N-terminal, cloned into pDEST17 vector (Gateway Cloning, Thermo Fisher Scientific Inc., Grand Island, NY), and used to transform DH5α E . coli chemically competent cells for ampicillin expression selection, as described before [21]. The plasmids with rMIC1-T126A/T220A and rMIC4-K469M were synthesized by GenScript (New Jersey, US) using a pET28a vector, and the MIC sequences carrying the mutations were cloned between the Nde I and Bam H I sites.…”

“…Importantly, the parasite’s Lac + subcomplex, consisting of MIC1 and MIC4, induces adherent spleen cells to release IL-12 [17], a cytokine critical for the protective response of the host to T. gondii infection [19]. In addition, immunization with this native subcomplex, or with recombinant MIC1 (rMIC1) and MIC4 (rMIC4), protects mice against experimental toxoplasmosis [20, 21]. The induction of IL-12 is typically due to detection of the pathogen by innate immunity receptors, including members of the Toll-like receptor (TLR) family, whose stimulation involves MyD88 activation and priming of Th1 responses, which protects the host against T. gondii [19, 22].…”

Epitope-based vaccine as a universal vaccination strategy against Toxoplasma gondii infection: A mini-review

“…Currently, the live attenuated tachyzoites of the strain S48 (commercially named "Toxovax") is the only approved vaccine for veterinary use. This vaccine was unfortunately shown limited efficacy [14].…”