Briefly, nitrocellulose bottom 96-well plates (MILLIPORE) were coated overnight at 4 °C with anti-IFN-γ monoclonal antibody (clone R4-6A2; Apoptosis inhibitor BD Biosciences) diluted in PBS. Plates were washed and blocked for 2 h with DMEM supplemented with 10% FCS. Spleen

cells of immunized mice were prepared in DMEM supplemented with 10% FCS and recombinant IL-2 (100 U/ml). Splenocytes were seeded at a density of 5 × 105 cells/well and stimulated with F3 antigenic fraction (5 μg/ml) during 20 h at 37 °C, 5% CO2. Plates were washed and incubated for 4 h, at room temperature, with a biotin-conjugate anti-mouse IFN-γ monoclonal antibody (clone XMG1.2; BD Biosciences) and, after the next wash step, with peroxidase-labeled streptavidin, for 2 h at room temperature. Reactions were detected with a peroxidase substrate containing 3,3′-diaminobenzidine Smad inhibitor tetrahydrochloride (1 mg/ml) and 30% hydrogen peroxide solution (1 μl/ml) in 50 mM Tris–HCL buffer, pH = 7.5. Reactions were stopped under running water, and spots were counted on a S5 Core ELISPOT Analyser (CTL). Four weeks after the boost immunization, mice were infected orally with 20 cysts of P-Br strain of T. gondii, obtained from macerated brains of infected Swiss-Webster reservoirs suspended in PBS. Animals were sacrificed 8 weeks after the challenge. The brains were collected, macerated and suspended in 1 ml of PBS. Cysts were counted, in

duplicates, under light microscope, in 10 μl of brain suspensions. All results were evaluated for their statistic significance by Student’s t-test (parametric data) or by Mann–Whitney test (non-parametric data) performed with Minitab version 14. Normal distribution of samples was assessed by Anderson Darling software. The recombinant NA38-SAG2 segment was developed to carry the SAG2 sequence of T. gondii flanked by the duplicated 3′ promoter and the extended native 5′ terminal sequence of 70 nucleotides corresponding to 28 nt of the 5′ promoter and a duplication

of the below last 42 nt of the NA coding sequence, located upstream the promoter ( Fig. 1). Recombinant Influenza A viruses harboring the dicistronic NA38-SAG2 segment (FLU-SAG2) were generated using the 12 plasmid-driven reverse genetics, as previously described [41]. Recombinant FLU-SAG2 viruses displayed a slightly altered phenotype ( Fig. 2A), but showed infectious titers (9.2 ± 3.2 × 107 pfu/ml) similar to wild type vNA (1.4 × 108 pfu/ml). The presence of SAG2 in recombinant NA segments was assessed in three FLU-SAG2 clones by RT-PCR with primers that allowed the amplification of the entire region of insertion of SAG2. As shown in Fig. 2B, amplification products of the expected size (∼900 bp) were observed for all clones analyzed. Moreover, these amplicons were sequenced and showed no mutation in SAG2 sequence as well as in the internal 3′promoter (data not shown). Taking together, these results showed that FLU-SAG2 viruses are genetically stable in cell culture.