CXCL13/CXCR5 axis facilitates TFH expansion and correlates with disease severity in adults with immune thrombocytopenia

Abstract

Background: Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder defined by a diminished platelet count. ITP pathogenesis involves intricate changes to both cellular and humoral immunity. The pivotal roles of follicular helper T (TFH) cells in the maturations of B cells and the production of antibodies are well-established. However, the specific role of TFH to the immunopathogenesis of ITP remain incompletely understood. This study aimed to clarify the association of CXCL13/CXCR5 axis with TFH in adults with ITP.

Methods: A total of 97 ITP patients and 41 healthy controls were enrolled. CD4⁺CXCR5⁺ TFH, CD4⁺CXCR5⁺PD-1⁺ TFH, CD4⁺CXCR5⁺Foxp3⁺ follicular regulatory T cells (TFR), and desialylated platelets in peripheral blood were measured by flow cytometry. Plasma cytokines were assessed by enzyme-linked immunosorbent assay. CD4⁺ T cells cocultured with chemokine CXCL13 in vitro was performed for the measurement of TFH proliferation. Intracellular production of reactive oxygen species (ROS) was examined by dichlorodihydrofluorescein diacetate (DCFH-DA) probe staining.

Results: We observed a significant increase in circulating TFH and a marked decrease in circulating TFR in the entire ITP cohort. The ratio of TFH/TFR was elevated, accompanied by heightened levels of platelet desialylation, cytokines BAFF, HMGB1, and IL-21, while levels of IL-10 were downregulated in adults with ITP. Notably, patients with ITP exhibiting platelet count below 50 × 10⁹/L had dramatically elevated levels in both chemokine CXCL13 and its receptor CXCR5⁺ TFH compared to those with platelet count above 100 × 10⁹/L. High frequencies of TFH correlated with poor therapeutic response. Furthermore, in vitro CD4⁺ T cell proliferation assay demonstrated a CXCL13 dose-dependent increase in the frequencies in both CD4⁺CXCR5⁺ TFH and CD4⁺CXCR5⁺PD-1⁺ TFH from ITP patients. Intriguingly, DCFH-DA assay illustrated a significant enhancement in intracellular ROS generation in CXCR5⁺ T cell subsets, especially in CD4⁺CXCR5⁺PD-1⁺ TFH from 4 patients with ITP.

Conclusions: These results underscore the pivotal role of CXCL13/CXCR5 axis-drived TFH expansion in the pathogenesis of ITP, providing a potential disease severity biomarker.

Keywords: CXCL13/CXCR5 axis; Follicular helper T cell; Follicular regulatory T cell; Immune thrombocytopenia; Platelet.