Abstract
Lymphatic endothelial cells (LECs) present peripheral tissue antigens to induce T cell tolerance. In addition, LECs are the main source of sphingosine-1-phosphate (S1P), promoting naive T cell survival and effector T cell exit from lymph nodes (LNs). Autophagy is a physiological process essential for cellular homeostasis. We investigated whether autophagy in LECs modulates T cell activation in experimental arthritis. Whereas genetic abrogation of autophagy in LECs does not alter immune homeostasis, it induces alterations of the regulatory T cell (T reg cell) population in LNs from arthritic mice, which might be linked to MHCII-mediated antigen presentation by LECs. Furthermore, inflammation-induced autophagy in LECs promotes the degradation of Sphingosine kinase 1 (SphK1), resulting in decreased S1P production. Consequently, in arthritic mice lacking autophagy in LECs, pathogenic Th17 cell migration toward LEC-derived S1P gradients and egress from LNs are enhanced, as well as infiltration of inflamed joints, resulting in exacerbated arthritis. Our results highlight the autophagy pathway as an important regulator of LEC immunomodulatory functions in inflammatory conditions.
Highlights
lymph nodes (LNs) stromal cells (LNSCs) are CD45neg nonhematopoietic cells that play an important role in LN, blood, and lymphatic vessel architecture
Whereas blood endothelial cells (BECs) maintained negligible levels of intracellular light chain 3 (LC3)-II upon collagen-induced arthritis (CIA) development in LNs draining the site of immunization, both lymphatic endothelial cells (LECs) and fibroblastic reticular cells (FRCs) demonstrated a significant increase in intracellular LC3-II levels at different time points during CIA (Fig. 1 A)
These results were confirmed in LECs and FRCs sorted by flow cytometry from LNs draining the site of CIA induction in LC3-GFP mice (Mizushima et al, 2004)
Summary
LN stromal cells (LNSCs) are CD45neg nonhematopoietic cells that play an important role in LN, blood, and lymphatic vessel architecture. They include three main subsets, the blood endothelial cells (BECs; gp38−CD31+), the fibroblastic reticular cells (FRCs; gp38+CD31−), and the lymphatic endothelial cells (LECs; gp38+CD31+; Rodda et al, 2018). LNSC functions are not restricted to their architectural role. They regulate T cell immunity, notably by altering dendritic cell (DC) maturation and migration (Buettner and Bode, 2011; Podgrabinska et al, 2009). LNSCs ectopically express self-antigens (Ags) restricted to peripheral tissues ( known as peripheral tissue Ags [PTAs]). The cross-presentation of exogenous Ags by LECs primes a small fraction of naive CD8+
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