Figure 2.

Histopathological confirmation of humoral rejection. (A) Representative photomicrographs of BALB/c hearts explanted at d50 from BL/6 Tcrbd^−/− recipients (reconstituted with 10³ wild-type [WT] TCR75 CD4 T cells) demonstrate: inflammatory infiltrates with myocyte loss and replacement fibrosis (on H&E staining); endothelial complement C4d deposition and areas of CD68⁺ (macrophage) and NK1.1⁺ (NK cell) staining, compared with grossly normal histology and negative staining in equivalent grafts from unmodified (not reconstituted) BL/6 Tcrbd^−/− recipients and BL/6 Tcrbd^−/− recipients reconstituted with Sh2d1a^−/− (SAP^−/−) TCR75 CD4 T cells. Representative photomicrographs of (B) elastin van Gieson stained sections of d50 allografts from the wild-type reconstituted group depicting fibroproliferative arterial intimal thickening, compared to control unmodified Tcrbd^−/− recipients, and (C) H&E stained sections demonstrating inflammatory infiltrates consisting predominantly of (left) polymorphs and (right) occasional plasma cells (arrows). (D) Representative photomicrographs of immunofluorescence staining showing interstitial capillary/vascular staining (arrowed) for C4d (red) and IgG deposition (green) in BALB/c cardiac allografts explanted at days 14 and 50 from BL/6 Tcrbd^−/− recipients reconstituted with 10³ WT TCR75 CD4 T cells, and at day 50 from WT reconstituted Rag2^−/− recipients. Intensity of C4d and IgG staining increased from day 14 to day 50 in Tcrbd^−/− recipients reconstituted with WT TCR75 CD4 T cells. All images are representative of at least 5 animals: scale bars–A: 50 μm (H&E, CD68, and NK1.1 images, except for the NK1.1 image of the reconstituted BL/6 Tcrbd^−/− group which is at 75 μm) or 100 μm (C4d images), B: 100 μm, C: 150 μm, and D: top row; scale bar-−50 μm; bottom row; scale bar−100 μm.