The immune landscape of the inflamed joint defined by spectral flow cytometry
Authors: Attrill Meryl H , Shinko Diana , Alexiou Vicky , Kartawinata Melissa ,   CHARMS study, Al-Abadi Eslam , Alexiou Vicky , Allen Cherelle , Armon Kate , Begum Rehana , Begum Rumena , Bostock Mariejennelynn , Buerkle Katrin , Busby Charlotte , Butt Maryam , Cheng Nga Sze (Emily) , Chou Chia-Ping , Cobb Joanna , Coke Louise , Cook Julie , Crook Jenny , Cruickshank-Hull Serena , Davies Karen , Dawson Lucinda , Dekaj Fatjon , Dimitrova Monika , Enright Julie , Etheridge Angela , Fofana Elizabeth (Lizzie) , Foster Sara , Foxall Sophie , Gilbert Paul , Gottschalk Genevieve , Hahn Eileen , Hall Jeannette , Hawley Daniel , Hinks Anne , Hirani Shashi , Howman Ruth , Hussein Alisha , Jeraj Fatema , Jordan Emma , Kartawinata Melissa , Kassoumeri Laura , Kimonyo Aline , Kupiec Klaudia , Lal Sham , Leahy Alice , Feilding Freya Luling , MacDonald Ian , McNeece Alyssia , Melville Laura , Moncrieffe Halima , Moore Gudrun , Mulligan Kathleen , Newman Stanton , Nguyen Lucy , Patrick Fiona , Peckham Hannah , Ralph Elizabeth , Rikunenko Rachel , Robinson Emily , Sharp Jennie , Southwood Taunton , Sowter Jason , Ullah Mohammed Zaffar , Thomson Wendy , Ursu Simona , Varsani Hemlata , Warrier Kishore , Wedderburn Lucy R , Whitworth Pamela , Wiffen Rachel , Wormal Alexis ,   JIAP study, Atrill Meryl , Alexiou Vicky , Allen Cherelle , Begum Rehana , Begum Rumena , Butt Maryam , Crook Jenny , Cruickshank-Hull Serena , Dawoud Hameedah , Dawson Lucinda , Etheridge Angela , Gottschalk Genevieve , Hahn Eileen , Jebson Beth , Jeraj Fatema , Johnson Cerise , Jordan Emma , Kartawinata Melissa , Kassoumeri Laura , Kaya Seyda , Kimonyo Aline , Kupiec Klaudia , Feilding Freya Luling , Foxall Sophie , MacDonald Ian , McGowan Ruth , McNeece Alyssia , Moncrieffe Halima , Nguyen Lucy , Patel Alka , Patrick Fiona , Peckham Hannah , Pesenacker Anne M , Pils Chad , Ralph Elizabeth , Robinson Emily , Rosser Lizzy , Tonye-Brown Opuriche (Riche) , Ursu Simona , Varsani Hemlata , Wedderbur Lucy R , Wedderburn Lucy R , Pesenacker Anne M 
Published: August 2024

Abstract
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 characterized 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.