Background/Purpose: Systemic Lupus Erythematosus (SLE) is characterized by the generation of autoantibodies that promote tissue injury. The development of pathogenic autoantibody-secreting B cells in lupus requires T follicular helper (Tfh) cells. Tfh cells are expanded in lupus patients with active disease and produce the cytokines IL-21 and IFN-γ that drive B cell differentiation into double negative memory (DN2) B cells, which become autoantibody-secreting cells. The regulation of pathogenic cytokine production in Tfh cells and a way to specifically target the subset producing IL-21 and IFN-γ is unknown. CD9 is a tetraspanin, shown to accumulate on activated CD4⁺ T cells at the immunological synapse, playing a role in their cytokine production. We identified a novel CD9-expressing Tfh cell population and assessed their role in lupus pathogenesis.

Methods: The frequency of CD9⁺ Tfh cells and their IL-21 and IFN-γ production was measured by flow cytometry from B6.Sle1.Yaa lupus mice at 2, 4, and 6 months of age. For assessing CD9⁺ circulating Tfh (cTfh) cells and DN2 B cells from patients with SLE, PBMCs were collected from patients on low doses of prednisone and hydroxychloroquine and excluding participants on immunomodulatory agents. DN2 B cell and cTfh cell phenotypes were assessed by flow cytometry or functionally by co-culturing experiments.

Results: We identified a distinct CD9-expressing Tfh cell (CD9⁺) population in murine lupus and found that they were the primary population of IL-21 and IFN-γ secreting-Tfh cells (Fig 1A, B). Comparison of CD9^– and CD9⁺ Tfh cells revealed that CD9⁺ Tfh cells were more migratory to the chemokines CXCL12 and CXCL13 and expressed elevated levels of the integrin VLA-4. RNA and ATAC sequencing showed that compared to the CD9^– population, CD9⁺ Tfh cells are a transcriptionally and epigenetically distinct population with increased cellular activation and effector Tfh cell function. Furthermore, the deletion of CD9 did not alter Tfh cell development but led to reduced IL-21 and IFN-γ production from Tfh cells and a specific decrease in the frequency of pathogenic DN2 B cells. We next assessed CD9⁺Tfh cells from the PBMCs of SLE patients and found an expansion of CD9⁺ cTfh cells and CD9⁺ T peripheral helper (Tph) cells compared to healthy controls (Fig 1C). The increased frequency of CD9⁺ cTfh cells in lupus patients was positively correlated to the increased DN2 B cell population. Moreover, co-culturing CD9⁺ or CD9^– cTfh cells with DN2 B cells from lupus patients demonstrated that these B cells required the CD9⁺ cTfh and not CD9^– cTfh cells for survival.

Conclusion: CD9 on Tfh cells identifies the pathogenic cytokine-producing population and regulates Tfh cell cytokine production. Additionally, CD9⁺ Tfh cells are an enhanced effector Tfh cell subset compared to the CD9^– population. CD9⁺ Tfh cells remain elevated throughout the disease in murine lupus and are increased in the circulation of lupus patients, enhancing the survival of DN2 B cells. This data supports the conclusion that the CD9⁺ Tfh cell subset may be critical for driving disease and provides the foundation for generating novel targeted therapeutic interventions and diagnostic techniques targeting pathogenic Tfh cells.

« Back to ACR Convergence 2024

ACR Meeting Abstracts - https://acrabstracts.org/abstract/cd9-expressing-t-follicular-helper-cells-are-a-highly-functional-subset-expanded-in-systemic-lupus-erythematosus/