EXPERIMENTAL IMMUNOBIOLOGY

X. Xu¹, C. Wynn¹, F. Pan¹, G. Xia¹, T. Yamada¹, K. Tamura¹, H. Jiang^2
1Transplant Immunology, Astellas Research Institute, Skokie/UNITED STATES OF AMERICA, ²Transplant Immunology, Astellas Research Institute, Skokie/IL/UNITED STATES OF AMERICA

Body: Aims: Allograft vasculopathy (AV) has emerged as the leading obstacle towards long-term survival of organ transplants. AV is generally believed to be mediated by T cells, but the role of B cells and alloantibodies (alloAbs) remains controversial. We sought to determine whether alloantibodies, T cells or B cells can independently contribute to the development of AV.

Methods: A single injection of MACS-purified B6 T cells (10⁷ cells/mouse) or B cells (3x10⁷ cells/mouse) was performed immediately after Balb/c aorta transplantation into B6 Rag1^-/- mice. Anti-donor IgG alloAbs were purified through protein G columns from positive sera harvested from wt B6 mice with a previously rejected Balb/c heart graft. Four injections of anti-Balb/c IgG alloAbs (250 g, i.v., twice a wk during a 2-wk period) was performed in Balb/c aorta transplanted B6 Rag1^-/- mice. Aorta grafts were harvested on d+15 and d+30 post-transfer and were subjected to histological and immunohistological analysis. Intimal proliferation or thickening was quantified by digital morphometry.

Results: Adoptive transfer of wt B6 T cells resulted in severe neointimal formation (more than 50% occlusion) on d+15 or d+30 and intense infiltration of mononuclear cells, including CD3⁺ T cells (primarily concentrated in the media and adventitial areas), but no CD19⁺ B cells were characterized. A 10-day treatment of FK506 (3 mg/kg/d) in the T cell-transferred recipients resulted in a marginal reduction of neointimal formation and decreased CD3⁺ T cell infiltration compared to the untreated control (T cell-transferred only) on d+15 after allografting. Adoptive transfer of B6 B cells showed infiltration of some CD19⁺ B cells but no sign of neointimal proliferation on d+15 or d+30. Mild neointimal proliferation (less than 25% occlusion) was observed in anti-Balb/c IgG-injected mice when examined on d+15 but the lesion was lessened when examined on d+30 post-transfer. There were no CD3⁺ T cells or CD19⁺ B cells demonstrated in aorta allografts of anti-Balb/c IgG -transferred recipients.

Conclusion: Our data support an independent role of alloantibody in the development of AV besides the contribution of T cells. The role of B cells (without T cell help) seems not to be directly required for the development of AV in our transplant setting.

Disclosure: All authors have declared no conflicts of interest.