The immune landscape of the inflamed joint defined by spectral flow cytometry.

Cellular phenotype and function are altered in different microenvironments. For targeted therapies it is important to understand site-specific cellular adaptations. Juvenile Idiopathic Arthritis (JIA) is characterised by autoimmune joint inflammation, with frequent inadequate treatment responses. To comprehensively assess the inflammatory immune landscape, we designed a 37-parameter spectral flow cytometry panel delineating mononuclear cells from JIA synovial fluid (SF) of autoimmune inflamed joints, compared to JIA and healthy control blood. Synovial monocytes and NK cells (CD56bright) lack Fc-receptor CD16, suggesting antibody-mediated targeting may be ineffective. B cells and DCs, both in small frequencies in SF, undergo maturation with high 4-1BB, CD71, CD39 expression, supporting T cell activation. SF effector and regulatory T cells were highly active with newly described co-receptor combinations that may alter function, and suggestion of metabolic reprogramming via CD71, TNFR2 and PD-1. Most SF effector phenotypes, as well as an identified CD4-Foxp3+ T cell population, were restricted to the inflamed joint, yet specific SF-predominant CD4+Foxp3+ Treg subpopulations were increased in blood of active but not inactive JIA, suggesting possible recirculation and loss of immunoregulation at distal sites. This first comprehensive dataset of the site-specific inflammatory landscape at protein level will inform functional studies and the development of targeted therapeutics to restore immunoregulatory balance and achieve remission in JIA.

Attrill MH ，Shinko D ，Alexiou V ，Kartawinata M ，Study CHARMS ，Study JIAP ，Wedderburn LR ，Pesenacker AM ... -  《-》

Differential Accumulation and Activation of Monocyte and Dendritic Cell Subsets in Inflamed Synovial Fluid Discriminates Between Juvenile Idiopathic Arthritis and Septic Arthritis.

Despite their distinct etiology, several lines of evidence suggest that innate immunity plays a pivotal role in both juvenile idiopathic arthritis (JIA) and septic arthritis (SA) pathophysiology. Indeed, monocytes and dendritic cells (DC) are involved in the first line of defense against pathogens and play a critical role in initiating and orchestrating the immune response. The aim of this study was to compare the number and phenotype of monocytes and DCs in peripheral blood (PB) and synovial fluid (SF) from patients with JIA and SA to identify specific cell subsets and activation markers associated with pathophysiological mechanisms and that could be used as biomarkers to discriminate both diseases. The proportion of intermediate and non-classical monocytes in the SF and PB, respectively, were significantly higher in JIA than in SA patients. In contrast the proportion of classical monocytes and their absolute numbers were higher in the SF from SA compared with JIA patients. Higher expression of CD64 on non-classical monocyte was observed in PB from SA compared with JIA patients. In SF, higher expression of CD64 on classical and intermediate monocyte as well as higher CD163 expression on intermediate monocytes was observed in SA compared with JIA patients. Moreover, whereas the number of conventional (cDC), plasmacytoid (pDC) and inflammatory (infDC) DCs was comparable between groups in PB, the number of CD141+ cDCs and CD123+ pDCs in the SF was significantly higher in JIA than in SA patients. CD14+ infDCs represented the major DC subset in the SF of both groups with potent activation assessed by high expression of HLA-DR and CD86 and significant up-regulation of HLA-DR expression in SA compared with JIA patients. Finally, higher activation of SF DC subsets was monitored in SA compared with JIA with significant up-regulation of CD86 and PDL2 expression on several DC subsets. Our results show the differential accumulation and activation of innate immune cells between septic and inflammatory arthritis. They strongly indicate that the relative high numbers of CD141+ cDC and CD123+ pDCs in SF are specific for JIA while the over-activation of DC and monocyte subsets is specific for SA.

Cren M ，Nziza N ，Carbasse A ，Mahe P ，Dufourcq-Lopez E ，Delpont M ，Chevassus H ，Khalil M ，Mura T ，Duroux-Richard I ，Apparailly F ，Jeziorski E ，Louis-Plence P ... -  《Frontiers in Immunology》

CD4+CD25bright regulatory T cells actively regulate inflammation in the joints of patients with the remitting form of juvenile idiopathic arthritis.

de Kleer IM ，Wedderburn LR ，Taams LS ，Patel A ，Varsani H ，Klein M ，de Jager W ，Pugayung G ，Giannoni F ，Rijkers G ，Albani S ，Kuis W ，Prakken B ... -  《JOURNAL OF IMMUNOLOGY》

Impaired suppression of synovial fluid CD4+CD25- T cells from patients with juvenile idiopathic arthritis by CD4+CD25+ Treg cells.

Natural CD4+CD25+FoxP3+ Treg cells play a crucial role in maintaining immune homeostasis and controlling autoimmunity. In patients with juvenile idiopathic arthritis (JIA), inflammation occurs despite the increased total numbers of Treg cells in the synovial fluid (SF) compared to the peripheral blood (PB). This study was undertaken to investigate the phenotype of CD4+ T cells in PB and SF from JIA patients, the function of synovial Treg cells, and the sensitivity of PB and SF CD4+CD25- effector T cells to the immunoregulatory properties of Treg cells, and to study the suppression of cytokine secretion from SF effector T cells by Treg cells. The phenotypes of effector T cells and Treg cells of PB and SF from JIA patients and healthy donors were determined by flow cytometry. The functionality of isolated Treg cells and effector T cells was quantified in (3) H-thymidine proliferation assays. Cytokine levels were analyzed using Bio-Plex Pro assay. Compared to PB, SF showed significantly elevated numbers of activated and differentiated CD4+CD45RO+ T cells. Sensitivity of SF effector T cells to the suppressive effects of Treg cells from both PB and SF was impaired, correlating inversely with the expression of CD69 and HLA-DR. However, SF effector T cell cytokine secretion was partly suppressed by SF Treg cells. Our findings indicate that regulation is impaired in the SF of patients with JIA, as shown by the resistance of effector T cells to immunoregulation by functional Treg cells. This resistance of the SF effector T cells might be due to their activated phenotype.

Haufe S ，Haug M ，Schepp C ，Kuemmerle-Deschner J ，Hansmann S ，Rieber N ，Tzaribachev N ，Hospach T ，Maier J ，Dannecker GE ，Holzer U ... -  《-》

TCR repertoire sequencing identifies synovial Treg cell clonotypes in the bloodstream during active inflammation in human arthritis.

The imbalance between effector and regulatory T (Treg) cells is crucial in the pathogenesis of autoimmune arthritis. Immune responses are often investigated in the blood because of its accessibility, but circulating lymphocytes are not representative of those found in inflamed tissues. This disconnect hinders our understanding of the mechanisms underlying disease. Our goal was to identify Treg cells implicated in autoimmunity at the inflamed joints, and also readily detectable in the blood upon recirculation. We compared Treg cells of patients with juvenile idiopathic arthritis responding or not to therapy by using: (i) T cell receptor (TCR) sequencing, to identify clonotypes shared between blood and synovial fluid; (ii) FOXP3 Treg cell-specific demethylated region DNA methylation assays, to investigate their stability and (iii) flow cytometry and suppression assays to probe their tolerogenic functions. We found a subset of synovial Treg cells that recirculated into the bloodstream of patients with juvenile idiopathic and adult rheumatoid arthritis. These inflammation-associated (ia)Treg cells, but not other blood Treg cells, expanded during active disease and proliferated in response to their cognate antigens. Despite the typical inflammatory-skewed balance of immune mechanisms in arthritis, iaTreg cells were stably committed to the regulatory lineage and fully suppressive. A fraction of iaTreg clonotypes were in common with pathogenic effector T cells. Using an innovative antigen-agnostic approach, we uncovered a population of bona fide synovial Treg cells readily accessible from the blood and selectively expanding during active disease, paving the way to non-invasive diagnostics and better understanding of the pathogenesis of autoimmunity.

Rossetti M ，Spreafico R ，Consolaro A ，Leong JY ，Chua C ，Massa M ，Saidin S ，Magni-Manzoni S ，Arkachaisri T ，Wallace CA ，Gattorno M ，Martini A ，Lovell DJ ，Albani S ... -  《-》