Effect of Clonally Expanded <scp>PD‐1<sup>high</sup>CXCR5</scp>–<scp>CD4</scp>+ Peripheral T Helper Cells on B Cell Differentiation in the Joints of Patients With Antinuclear Antibody–Positive Juvenile Idiopathic Arthritis
Jonas Fischer, Johannes Dirks, Julia Klaussner, Gabriele Haase, Annette Holl‐Wieden, Christine Hofmann, Stephan Hackenberg, Hermann Girschick, Henner Morbach
Abstract
Objective Antinuclear antibody (ANA)–positive juvenile idiopathic arthritis (JIA) is characterized by synovial B cell hyperactivity, but the precise role of CD4+ T cells in promoting local B cell activation is unknown. This study was undertaken to determine the phenotype and function of synovial CD4+ T cells that promote aberrant B cell activation in JIA. Methods Flow cytometry was performed to compare the phenotype and cytokine patterns of PD‐1 high CD4+ T cells in the synovial fluid (SF) of patients with JIA and T follicular helper cells in the tonsils of control individuals. TCRVB next‐generation sequencing was used to analyze T cell subsets for signs of clonal expansion. The functional impact of these T cell subsets on B cells was examined in cocultures in vitro. Results Multidimensional flow cytometry revealed the expansion of interleukin‐21 (IL‐21) and interferon‐γ (IFNγ)–coexpressing PD‐1 high CXCR5–HLA–DR+CD4+ T cells that accumulate in the joints of ANA‐positive JIA patients. These T cells exhibited signs of clonal expansion with restricted T cell receptor clonotypes. The phenotype resembled peripheral T helper (Tph) cells with an extrafollicular chemokine receptor pattern and high T‐bet and B lymphocyte–induced maturation protein 1 expression, but low B cell lymphoma 6 expression. SF Tph cells, by provision of IL‐21 and IFNy, skewed B cell differentiation toward a CD21 low/– CD11c+ phenotype in vitro. Additionally, SF Tph cell frequencies correlated with the appearance of SF CD21 low/– CD11c+CD27–IgM– double‐negative (DN) B cells in situ. Conclusion Clonally expanded CD4+ Tph cells accumulate in the joints of ANA‐positive JIA patients and, in particular, promote CD21 low/– CD11c+ DN B cell differentiation. The expansion of Tph cells and DN B cells might reflect the autoimmune response in the joints of ANA‐positive JIA patients.