Cells were washed after 48 hr and lysed for 30 min at 4° in radioimmunoprecipitation assay buffer [1% Triton X-100 (v/v), 0·5% sodium deoxycholate (w/v), 0·1% SDS] containing protease inhibitor cocktail (Sigma-Aldrich). Cell debris was spun down at 15 600 g
for 15 min. Precipitates were removed and aliquots of cell lysates were diluted in SDS sample buffer, boiled at 100° for 3 min, spun down, and applied to precast 10% acrylamide Tris–glycine gels at 40 g protein/lane and run at 150 V for 1 hr. Samples were transferred to nitrocellulose membrane (BioRad) at 100 V for 1 hr. Membranes were probed using rabbit anti-mouse Arg I polyclonal antibody (Santa Cruz Biotechnology, HM781-36B order Santa Cruz, CA) and rabbit anti-mouse iNOS (NOS2) polyclonal antibody
(BD Biosciences) at a 1 : 500 and 1 : 2000 dilutions, respectively, followed by peroxidase-conjugated anti-rabbit antibody (Sigma-Aldrich) at a 1 : 1000 dilution. Bands were visualized using a chemiluminescence reaction. Splenocytes were prepared from naive mice, and enriched for CD90.2+ cells (90% by FACS analysis) using anti-FITC-coated magnetic beads (MACS; Miltenyi Biotec, Bergisch Gladbach, Germany) after incubation with FITC-conjugated anti-CD90.2 mAb. Peritoneal cells were enriched for F4/80+ Mφs (85% by FACS analysis) using anti-FITC-coated KU-60019 magnetic beads (MACS; Miltenyi Biotec) after incubation with FITC-conjugated anti-F4/80 mAb. The T-cell proliferative response was evaluated after co-culturing CD90.2+ spleen cells (2 × 105 cells/200 μl/well) with F4/80+ peritoneal cells in flat-bottom microwell tissue Oxymatrine culture
plates at different T-cell/ Mφ ratios (2 : 1, 5 : 1, 10 : 1 and 20 : 1) in the presence of 2.5 μg/ml concanavalin A (Con A; Sigma-Aldrich). The presence of naive Mφs increased proliferation of CD90.2+ T cells and the most effective Mφ-to-T-cell ratio was 1 : 10 (data not shown). The PD-1/PD-Ls pathway blockade on the proliferative response was evaluated after co-culturing CD90.2+ spleen cells (2 × 105 cells/200 μl/well) with infected or non-infected F4/80+ peritoneal cells in flat-bottom microwell tissue culture plates treated with 5 μg/ml isotype control, anti-PD-1, anti-PD-L1 or anti-PD-L2 in the presence of 2.5 μg/ml Con A (Sigma-Aldrich). Cultures were maintained at 37° in a humidified 5% CO2 atmosphere for 3 days and 0·5 μCi/well [methyl-3H] thymidine (Amersham, Chicago, IL) was added for the last 18 hr of culture. Cells were collected with a cell harvester (Cambridge Technology, Watertown, MA) and processed for standard liquid scintillation counting using a counter from Beckman Instruments (Fullerton, CA). Values are represented as counts per minute from triplicate wells. The T. cruzi-infected and non-infected peritoneal cells were obtained and single cell suspensions were prepared in RPMI-1640 supplemented as above.