Purpose Primary antiphospholipid syndrome (PAPS) is an autoimmune disorder characterized by the presence of pathogenic autoantibodies directed against membrane phospholipids and/or their associated plasma proteins. Current evidence suggests that immunocytes are involved in the thrombotic event and adverse pregnancy outcomes in APS. The incomplete understanding of the precise cellular and molecular events that drive disease activity poses a significant hurdle to the development of targeted therapeutic agents and predicting the prognosis. To achieve a single-cell systems-level perspective of APS immunopathogenesis, we leveraged the high-dimensionality of mass cytometry to (1) assess peripheral blood mononuclear cell profiles in different clinical phenotypes of APS and controls, (2) validate the function of the noteworthy cell subpopulations.
Method A total of 20 PAPS patients were recruited for this study. All the PAPS patients were newly diagnosed by 2006 Sydney APS criteria from November 2021 to March 2022 in Pecking Union Medical College Hospital. In addition to the typical clinical symptoms, these patients had high titers of IgG for triple antiphospholipid antibodies (APL) positive and had never received treatment. Meanwhile, 4 age and sex-matched healthy people were selected as controls (HC). EDTA anticoagulated venous blood samples were collected from each participant. Peripheral blood mononuclear cells (PBMCs) were isolated by density-gradient centrifugation with Ficoll. The concentration of samples was adjusted to 1*106/mL. Mass cytometry (CyTOF) was performed to detect the expression intensity of PBMC surface markers. CyTOF data was analyzed using FlowJo software and R package. Comparisons between groups were performed using Mann-Whitney U test and One-way ANOVA.
Results we mapped a comprehensive immunological profile of PBMCs from patients with primary thrombotic APS (TAPS) and primary obstetric APS (OAPS). Our findings showed that all PAPS patients have reduced T cell expression compared with HC (p=0.019). The overall T cells decreased mainly in the TAPS patients, where the proliferation/activated CD8+ cytotoxic T cells reduced, such as CD8+CD127+Tbet+ T cells (TAPS vs. HC = 0.015). However, in the OAPS group, the expression of activated CD8+ cytotoxic T cells was significantly increased compared to both TAPS and HC (CD8+Tbet+Fas+, OAPS vs. HC p = 0.0046; OAPS vs. TAPS p = 0.0011). We found that the B cell subset in OAPS group have a significantly different distribution from TAPS and HC. And we identified a distinct increased Tbet+CD11chigh B cell subset in OAPS patients (OAPS vs. HC p = 0.0065; OAPS vs. TAPS p = 0.033).
Conclusions These results suggest that triple APL-positive patients with different clinical subtypes of PAPS have their own specific immune cell expression. The high expression of Tbet+CD11chigh B cell may be involved in the pathological pregnancy process and closely linked to disease development in OAPS patients. The proliferation/activated CD8+ cytotoxic T cell is more likely to play a role in regulating the peripheral differentiation process of the Tbet+CD11chigh B cell subset.
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