Introduction: The kidney is pro-tolerogenic by mechanisms as yet unknown. In mice, tolerance of kidney allografts can occur spontaneously in certain strain combinations, such as DBA/2 to C57/BL6. We have previously identified novel lymphoid structures in all accepted kidney grafts that may be important in tolerance induction and named them Treg-rich lymphoid structures (TOLS). Depletion of Tregs results in the dissolution of these structures, resulting in renal allograft rejection. Ectopic immune cell aggregates referred to as tertiary lymphoid organs (TLO) have been found in various chronic inflammatory conditions. Here we further investigated the time-course by which various immune cell types infiltrate in accepted mouse kidney allografts, the lymphoid characteristics and the functional properties of TOLS and how they differ from classical TLOs, as well as the mechanism of TOLS formation.Methods: DBA/2 kidneys were transplanted into C57/BL6 recipients. Transplanted animals were sacrificed at week 1, 3, 6 and 32 post-transplant. Immunohistochemical, pathologic, and flow cytometric analyses were performed to characterize the phenotype of graft cell infiltrates, including structural and functional properties. CCR7 knockout mice were also used as recipients to study possible underlining mechanism of TOLS formation. Results: We show that TOLS structures consist B and T cells, Tregs, conventional and plasmacytoid dendritic cells, and CD11b+ cells. TOLS are distinct from TLOs in that TOLS lack high endothelial venules. As these structures form, we see increased expression of podoplanin, a protein marker for lymphatics, within TOLS, suggesting that these structures are developing lymphatic-like characteristics. TOLS formation is dependent on the chemokine receptor, CCR7. Renal allografts in a CCR7 KO recipient exhibit much smaller TOLS with increased fibrosis and pathological evidence of rejection. RNA analysis show that the CCR7 ligand, CCL19, is highly expressed in accepted kidney allografts when compared to rejecting and native kidneys (p < 0.001). Conclusion: We show that TOLS are distinct from classical tertiary lymphoid organs, may be dependent on the CCR7/CCL19 pathway, and are characteristic of renal allograft acceptance.

CITATION INFORMATION: Yang C., Rosales I., O'Shea T., Ndishabandi D., White R., Russell P., Madsen J., Alessandrini A., Colvin R. Early Evolution and Pathologic Characteristics of Treg-Rich Organized Lymphoid Structures (TOLS) Associated with Immunological Tolerance in Accepted Mouse Kidney Allografts Am J Transplant. 2017;17 (suppl 3).

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