Fibroblastic Reticular Cells From Lymph Nodes Attenuate T Cell Expansion by Producing Nitric Oxide

Stefanie Siegert,Lucie Carrie,Peter J Nelson,Benjamin J Marsland,Dietmar Zehn,Hsin-Ying Huang,Chen-Ying Yang,Matthias Heikenwalder,Christopher D Buckley,Sanjiv A Luther,Hans Acha-Orbea,Sarah Essex,Leonardo Scarpellino

doi:10.1371/journal.pone.0027618

Abstract

Adaptive immune responses are initiated when T cells encounter antigen on dendritic cells (DC) in T zones of secondary lymphoid organs. T zones contain a 3-dimensional scaffold of fibroblastic reticular cells (FRC) but currently it is unclear how FRC influence T cell activation. Here we report that FRC lines and ex vivo FRC inhibit T cell proliferation but not differentiation. FRC share this feature with fibroblasts from non-lymphoid tissues as well as mesenchymal stromal cells. We identified FRC as strong source of nitric oxide (NO) thereby directly dampening T cell expansion as well as reducing the T cell priming capacity of DC. The expression of inducible nitric oxide synthase (iNOS) was up-regulated in a subset of FRC by both DC-signals as well as interferon-γ produced by primed CD8+ T cells. Importantly, iNOS expression was induced during viral infection in vivo in both LN FRC and DC. As a consequence, the primary T cell response was found to be exaggerated in Inos −/− mice. Our findings highlight that in addition to their established positive roles in T cell responses FRC and DC cooperate in a negative feedback loop to attenuate T cell expansion during acute inflammation.

Highlights

Adaptive immune responses are initiated most efficiently within secondary lymphoid organs (SLO), such as the spleen or lymph nodes (LN), where pathogens are filtered from body fluids and presented to recirculating T cells
Lymph node TRC dampen T cell expansion To dissect the role of TRC in T cell activation and differentiation, we initially adopted a reductionist approach: T cells were co-cultured with antigen-pulsed bone-marrow derived dendritic cells (DC) (BM-DC), either in the presence or absence of TRC
To study T cell priming CD45.1+ congenic ovalbumin (OVA)specific OT-I T cell receptor (TCR) transgenic CD8+ T cells were labeled with the proliferation dye carboxyfluorescein succinimidyl ester (CFSE), mixed with unspecific WT T cells (CD45.2+) in a ratio of 1:50, and cultured together with antigen-pulsed Bone marrow (BM)-DC on top of an adherent layer of the TRC line

Summary

Introduction

Adaptive immune responses are initiated most efficiently within secondary lymphoid organs (SLO), such as the spleen or lymph nodes (LN), where pathogens (or foreign antigens) are filtered from body fluids and presented to recirculating T cells. Dendritic cells (DC) residing in peripheral tissues capture foreign antigens and danger signals inducing their maturation, including up-regulation of the chemokine receptor CCR7 allowing DC to migrate via lymphatic vessels into the paracortex (T zone) of the draining SLO. There they present antigen-derived peptides in the context of surface MHC molecules to thousands of naıve recirculating T cells. The rare antigen-specific T cells become activated, start secreting cytokines and undergo multiple rounds of cell division They differentiate into effector cells and leave the LN as a large cohort that migrates to the site of inflammation [1,2,3,4]. TRC are the major constitutive source of IL-7 in LN and access to LN TRC is critical for naıve T cell survival [9,13]

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Conclusion