Figure 6.

Alloantibody mediates endothelial activation and complement deposition. (A) Representative photomicrographs of immunofluorescence staining with no evidence of interstitial capillary staining for C4d (red, left) and IgG deposition (green, right; scale bars−50 μm) in BALB/c cardiac allografts explanted (at day 50) from Rag2^−/− recipients reconstituted with 5 × 10⁵ TCR75 CD4 T cells. (B) Anti-H-2K^d IgG antibody (mean ± S.D.) in Rag2^−/− recipients of BALB/c allografts injected with day 50 serum pooled from either help-unlimited BL/6 Tcrbd^−/− (immune serum, n = 5) or help-unlimited Rag2^−/− recipients (control serum, n = 5). (C) Transfer of immune serum led to acute graft loss, whereas transfer of control serum resulted in indefinite heart allograft survival (P < 0.001, log-rank test). (D) Histology of explanted hearts (day 7) demonstrated widespread myocyte damage and endothelial C4d deposition following transfer of immune serum (left), in comparison with normal histology and negative staining at day 30 following control serum transfer (right). Images are representative of 3 animals; scale bars−100 μm (H&E) and 150 μm (C4d).