Toll Like Receptor 2 Mobilizes Regulatory T Cell Lymphatic Migration by Stimulating Lymphotoxin Expression

W. Piao¹, Y. Xiong², L. Li³, V. Saxena³, C. Paluskievicz³, J. Bromberg⁴

¹Microbiology and Immunology, U. Maryland, Baltimore, baltimore, MD, ²Surgery, U. Maryland, Baltimore, baltimore, MD, ³Surgery, U. Maryland, Baltimore, Baltimore, MD, ⁴Surgery and Microbiology and Immunology, U. Maryland, Baltimore, Baltimore, MD

Meeting: 2019 American Transplant Congress

Abstract number: 369

Keywords: CD4, Co-stimulation, Graft survival, Inflammation

Session Information

Session Name: Concurrent Session: Islet and Cell Transplantation

Session Type: Concurrent Session

Date: Monday, June 3, 2019

Session Time: 4:30pm-6:00pm

Presentation Time: 5:18pm-5:30pm

Location: Room 309

*Purpose: Regulatory T cell (Treg) afferent lymphatic migration is important for islet allograft survival. Treg express high levels of lymphotoxin (LT) and bind the LT beta-receptor (LTβR) on lymphatic endothelial cells (LEC). The Treg-LEC interaction modulates LEC function, which facilitates lymphatic migration. TLR2 is expressed in Treg, and its agonist Pam3CSK4 is linked to T cell survival, proliferation, and differentiation. Endogenous TLR2 ligands, such as hyaluronic acid (HA) and high mobility group proteins (HMGB), are released from transplanted islets and influence rejection through TLR2 stimulated inflammatory cytokine secretion. We tested the hypothesis that TLR2 signaling regulates Treg migration and function.

*Methods: Induced Treg (iTreg) were sorted from wild type (WT) or TLR2^-/-mice. Treg and activated CD4 were stimulated with T cell receptor (TCR) agonists or IL-2, with or without Pam3CSK4 (TLR2 agonist), LPS (TLR4), or R848 (TLR8). TCR or IL-2-induced classical NFκB and MAPK signaling were analyzed by immune blotting. T cells were analyzed for LT expression and for in vitro and in vivo migration. BALB/c islets were transplanted to C57BL/6 recipients.

*Results: CD4 subsets expressed different levels of TLR2. iTreg and activated nTreg showed the highest levels of surface TLR2, while unstimulated naïve and activated CD4 had lower or minimal TLR2. TLR2 signaling alone did not increase LT on Treg. However, TLR2 stimulation augmented TCR and IL-2-induced LT expression on Treg. Only TLR2, but not TLR4 or TLR8, activation enhanced LT expression on Treg. TLR2 stimulation promoted Treg trans-endothelial migration, but not migration of other T cell subsets. Phosphorylation of classical NFκB and ERK were induced in IL-2 stimulated Treg, and amplified by TLR2 co-stimulation. Challenging iTreg with allogenic pancreatic islets dramatically increased LTαβ expression and migration in WT, but not TLR2^-/- Treg, showing islets directly stimulated Treg via TLR2. WT, but not TLR2^-/-, Treg prolonged islet graft survival (median survival 34 vs 15 days, p<.05).

*Conclusions: TLR2 signaling preferentially promotes LT expression and Treg migration, which enhances their suppressive function. Islets express TLR2 ligands and directly stimulate Treg. These results demonstrate a previously unexplored link between TCR/IL-2R and TLR2 signaling in Treg that leads to modulation of LT expression and regulation of T cell lymphatic migration and suppression. The TLR2 agonist and antagonist are potential tools for regulating Treg function in tissues and protection of the allograft.

To cite this abstract in AMA style:

Piao W, Xiong Y, Li L, Saxena V, Paluskievicz C, Bromberg J. Toll Like Receptor 2 Mobilizes Regulatory T Cell Lymphatic Migration by Stimulating Lymphotoxin Expression [abstract]. Am J Transplant. 2019; 19 (suppl 3). https://atcmeetingabstracts.com/abstract/toll-like-receptor-2-mobilizes-regulatory-t-cell-lymphatic-migration-by-stimulating-lymphotoxin-expression/. Accessed May 18, 2025.

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