Introduction

Autoantibody following organ transplantation is increasingly correlated with poor graft outcome.We have reported recently that in a MHC class II mismatched mouse heart transplant model,graft-versus-host recognition by donor CD4 T cells is critical for development of humoral autoimmunity,but that the response is thereafter maintained by recipient CD4 T cells.Here we address the precise contribution of the recipient population to autoantibody production.

Methods

The role of donor and recipient CD4 T cells was investigated by transplanting MHC class II-disparate bm12 heart grafts with or without CD4 T cells into either wild type (WT) or T cell deficient (TCR^-/-) B6 mice.Germinal centres (GCs) were identified on immunofluorescence staining of splenic sections as PNA and Ly77 (GL7) positive B cell follicles.Autoantibody responses were analysed by Hep-2 staining.Diversification of humoral response was examined by anti-vimentin antibody ELISA at early and late time points.Chronic allograft vasculopathy (CAV) was assessed on EVG staining by quantifying degree of luminal stenosis.

Results

Transplantation of bm12 hearts into B6 recipients provoked production of long-lasting autoantibody and 68±3% of the splenic B cell follicles at week 7 had undergone GC differentiation.Autoantibody also developed following transplantation into TCR^-/- recipients,but without GC differentiation (8±2% of follicles),unless the recipient CD4 T cell population was restored by adoptive transfer of B6 CD4 T cells (55±2% of follicles).Interestingly,late (after 10 weeks) anti-vimentin autoantibody developed in WT recipients,but was only detectable in TCR^-/- recipients upon reconstitution with B6 CD4 T cells,suggesting that diversification of the humoral autoimmune response is dependent upon GC activity.Histological examination of the grafts revealed significant CAV only in recipients that also developed GCs(bm12 to B6 76±3%,bm12 to TCR^-/- with B6 CD4 T cells 72±9%;cf 1±1% in bm12 to TCR^-/- recipients).Finally, when CD4 T cell depleted bm12 donors were transplanted into B6 recipients, there was no autoantibody production, a lack of GCs and minimal CAV development (12±4%).

Conclusion

Donor and recipient CD4 T cells are essential for progression of allograft vasculopathy,most likely because of their cooperation to promote long-lasting GC autoantibody responses.These diversify to target additional, and potentially damaging, graft-related autoantigen.

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