Reporters of TCR signaling identify arthritogenic T cells in murine and human autoimmune arthritis

Abstract

How pathogenic CD4 T cells in Rheumatoid Arthritis (RA) develop remains poorly understood.We used Nur77-a marker of T cell antigen receptor (TCR) signaling-to identify antigenactivated CD4 T cells in the SKG mouse model of autoimmune arthritis and in patients with RA.Using a fluorescent reporter of Nur77 expression in SKG mice, we found that higher levels of Nur77-eGFP in SKG CD4 T cells marked their autoreactivity, arthritogenic potential, and ability to more readily differentiate into IL-17 producing cells. The T cells with increased autoreactivity, nonetheless had diminished ex vivo inducible TCR signaling, perhaps reflective of adaptive inhibitory mechanisms induced by chronic auto-antigen exposure in vivo. The enhanced autoreactivity was associated with upregulation of IL-6 cytokine signaling machinery, which might in part be attributable to a reduced amount of expression of suppressor of cytokine signaling 3 (SOCS3)-a key negative regulator of IL-6 signaling. As a result, the more autoreactive GFP hi CD4 T cells from SKGNur mice were hyper-responsive to IL-6 receptor signaling. Consistent with findings from SKGNur mice, SOCS3 expression was similarly downregulated in RA synovium. This suggests that, despite impaired TCR signaling, autoreactive T cells exposed to chronic antigen stimulation exhibit heightened sensitivity to IL-6 which contributes to the arthritogenicity in SKG mice, and perhaps in patients with RA.

Control of regulatory T‐cell differentiation and function by T‐cell receptor signalling and Foxp3 transcription factor complexes

“…showed that low concentrations of anti‐CD3 antibody (~0·5 µg/ml) together with IL‐2 and TGF‐β promoted Treg differentiation, while high concentrations (~5 µg/ml) rather suppressed Foxp3 expression and induced Th17 differentiation . Ashouri et al . used Nur77‐GFP reporter in an arthritis‐prone background and showed that Nur77‐GFP high cells are enriched with arthritogenic Th17 cells.…”

Impaired T cell receptor signaling and development of T cell–mediated autoimmune arthritis

“…In in vitro autologous mixed lymphocyte reaction (AMLR), self‐reactive SKG CD4SP mature thymocytes, and CD4 + T cells actively proliferated in response to self‐peptides/MHC complexes on APCs, whereas BALB/c WT CD4SP thymocytes or CD4 + T cells were scarcely responsive . Supporting these findings, GFP high , that is, highly self‐reactive, T cells in SKGNur mice described above were prone to differentiate in vivo into Th17 cells with arthritogenicity, and proliferated more robustly in AMLR compared with WTNur mice . Such AMLR also revealed that IL‐6 was predominantly produced by APCs, TNF‐α by both APCs and T cells, while IL‐17 was produced only by effector CD4 + T cells but not by CD4SP thymocytes .…”

“…Regardless of hyporesponsiveness to TCR stimulation due to Zap70 skg mutation, SKG mice harbor phenotypically activated CD4 + T cells presumably because of their high self‐reactivity. A recent study using Nur77 ( NR4a1 )‐eGFP as a reporter for TCR signaling strength in SKG and WT mice (SKGNur and WTNur mice, respectively) indeed demonstrated that self‐reactivity and arthritogenicity of peripheral CD4 + T cells were well correlated with the levels of Nur77 expression . For example, SKGNur mice had an increased number of CD44 high CD62L low effector/memory CD4 + T cells enriched in the GFP high population, which was also high in the arthritogenicity; adoptive transfer of GFP high T cells into severe combined immunodeficiency (SCID) mice induced early‐onset severe arthritis, in contrast with late‐onset milder arthritis by GFP low T cell transfer.…”

Developing Human Skin Contains Lymphocytes Demonstrating a Memory Signature

“…Strikingly, up to 30% of CD4 + Tconv and slightly fewer CD8 + T cells in fetal skin were CD45RO + (Figures 3A-3C). Higher levels of Nur77, a specific reporter of T cell receptor (TCR) signaling, [27][28][29] were detected in fetal CD45RO + versus CD45RA + cells, further suggesting antigen stimulation in this putative memory population (Figures 3D-3F).…”