Introduction: Our lab has demonstrated that murine kidney allografts are spontaneously accepted in specific donor-recipient strain combinations. Histologic examination of spontaneously accepted DBA/2J (DBA) kidneys into C57BL/6 (B6) recipients reveal organized lymphoid structures around the renal cortex that are dense in CD3+Foxp3+ T-regulatory cells and dendritic cells, which we term Treg rich organized lymphoid structures (TOLS). Here we further characterize the cellular composition of TOLS, and provide a potential mechanism for their induction.

Methods:

Transplants:

DBA/2, bm12, and bm1 kidneys were transplanted into C57/BL6 recipients post recipient bilateral nephrectomy. Recipients were sacrificed at week 1, 3, 6 and 32 post-transplant. Pathologic evaluation was performed through immunohistochemistry.

Treg Induction Assays:

pDCs were isolated from the bone marrow of mice, and co-cultured with naïve CD4+CD25- T cells isolated from the spleen in the presence and absence of IL-2 and TFG-beta for 4 days. Cultures were analyzed using flow cytometry.

Results:

Pathological analysis of spontaneously accepted DBA kidney allografts revealed the presence of PDCA-1+ cells in TOLS. We demonstrated that in vitro, DBA H2^d pDCs can induce a high level of FoxP3 expression when co-cultured with naïve B6 H2^b CD4+ T cells. This induction of FoxP3 was not observed in co-cultures using pDCs from donor strains that resulted in kidney allograft rejection. pDCs from bm12 mice, which are congenic to B6 except for an MHC class II mismatching through the H2-I-A^b locus, can induce Tregs from naïve B6 T cells in vitro, and, when transplanted into a B6 mouse, bm12 kidneys were spontaneously accepted with the development of TOLS. bm1 MHC class I mismatched kidneys are accepted, but did not form TOLS. pDCs from B6.NOD mice have H2^d genetics except for a g7 mutation at the H2-I-A^b locus and induce less Foxp3+ cells from naïve H2^b T cells compared to fully H2^d DBA pDCs.

Conclusion

Spontaneous murine renal allograft tolerance may be mediated by plasmacytoid dendritic cells in TOLS, that induce Tregs upon recognition of an allogeneic MHC Class II locus.

CITATION INFORMATION: O'Shea T., Yang C., Rosales I., Oh N., Ndishibandi D., Ashry T., Russell P., Madsen J., Colvin R., Alessandrini A. The Role of pDCs in Formation of Treg-Rich Organized Lymphoid Structures in Spontaneously Accepted Murine Kidney Allografts is Dependent on Mismatching of MHC Class II Molecules at the H2-I-A^b Locus Am J Transplant. 2017;17 (suppl 3).

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