Treg Lymphotoxin and Lymphatic Endothelial Cell Lymphotoxin Receptor Interactions Are Required for Treg Stability and Allograft Protection

V. Saxena, W. Piao, L. Li, C. M. Palusckievicz, Y. Xiong, T. Simon, J. S. Bromberg

U Maryland, Baltimore, MD

Meeting: 2019 American Transplant Congress

Abstract number: D148

Keywords: Endothelial cells, Graft survival, Mice, knockout, T cells

Session Information

Session Name: Poster Session D: Lymphocyte Biology: Signaling, Co-Stimulation, Regulation

Session Type: Poster Session

Date: Tuesday, June 4, 2019

Session Time: 6:00pm-7:00pm

Presentation Time: 6:00pm-7:00pm

Location: Hall C & D

*Purpose: Regulatory T cells (Treg) restrain allograft rejection through suppressor functions that are dependent upon expression of the transcription factor Foxp3, their proper migration, and their engagement with lymphotoxin beta receptor (LTβR). Using three unique genetic models, we tested the hypothesis that Treg-LTβR engagement is required for maintaining Foxp3 expression and Treg function of allograft protection.

*Methods: Mice with deletion of lymphotoxin alpha (LTα^-/-); LTβR^-/-; and Prox1-Cre-ER^T2+/-LTβR^fl/fl (KO^fl) mice, in which LTβR is depleted in lymphatic endothelial cells (LEC) by tamoxifen treatment, were used. Treg stability, migration and function were analyzed in vivo in an islet allograft model, and in vitro in an LEC migration assay.

*Results: Treg use LTαβ to stimulate LTβR on LEC for migration to draining lymph nodes (dLN) via afferent lymphatics. Conditional or germline depletion of LTα or LTβR prevented Treg lymphatic migration from tissues to dLN. In an islet allograft model, depletion of LTβR on LEC, or deletion of LTα on Treg, led to Treg retention in the graft and poor migration to the dLN. Treg differentiation and execution of their suppressor function required sequential migration from the target tissue to the dLN. Modulation of LTβR on LEC or LTαβ on Treg resulted in downregulation of Foxp3 expression in Treg and generation of exTreg. Disruption of LTαβ-LTβR interactions between Treg and LEC resulted in impaired allograft survival from 23d to 14d in KO^fl mice (p<.03) and to 13d in LTβR^-/- (p<.03) mice. In a transwell based Treg-LEC co-culture assay, migrating Treg maintained high Foxp3 expression, while non-migrating Treg lost Foxp3, CD25, CD44, CD49b, CD69 and LTαβ expression to become exTreg.

*Conclusions: Treg use LTαβ-LTβR for sequential migration from the target tissues to dLN. This migration is important for Treg differentiation and suppressive function. Any disruption in the LTαβ-LTβR interaction results in poor migration, increased retention in graft, loss of Foxp3 expression, and thereby their ability for allograft protection. The exTreg have the potential to become T effector cells and cause allograft rejection. Treg-LEC LTαβ-LTβR interactions are important for Treg stability and suppressor function.

To cite this abstract in AMA style:

Saxena V, Piao W, Li L, Palusckievicz CM, Xiong Y, Simon T, Bromberg JS. Treg Lymphotoxin and Lymphatic Endothelial Cell Lymphotoxin Receptor Interactions Are Required for Treg Stability and Allograft Protection [abstract]. Am J Transplant. 2019; 19 (suppl 3). https://atcmeetingabstracts.com/abstract/treg-lymphotoxin-and-lymphatic-endothelial-cell-lymphotoxin-receptor-interactions-are-required-for-treg-stability-and-allograft-protection/. Accessed May 10, 2025.

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