Background: The antiphospholipid syndrome (APS) is an acquired autoimmune disorder characterized by thrombotic events, obstetric morbidity and a myriad of systemic manifestations induced by the persistent presence of autoantibodies directed against phospholipids or phospholipid- binding proteins (aPLs).

Patients and Methods: The following patient’s groups were enrolled a) Primary APS (APS-I n=19), b) Secondary APS (related to other autoimmune disorder, frequently SLE, APS-II n=17), c) Immunoserological positivity for aPLs without clinical manifestation (APS-III n=16). Healthy controls, that were age and gender matched subjects. PBMCs were purified by density gradient centrifugation using Leucosep tubes. For the understanding of single cell heterogeneity in APS flow cytometric immunophenotyping of peripheral blood was performed using the Cytek Aurora full spectrum profiling system. The optimized multicolor immunofluorescence panel consisted of 25 markers, such as: CD45RA, CD20, CD141, CD8, CD14, HLA-DR, CD25, CD4, CD16, IgD, TCRγ/δ, CD11c, CD127, CD1c, CD19, CD123, CD45, CD27, CD197, IgM, CD3, CD28, CD38, CD56, CD279. The spectral cytofluorimeter, the Cytek Aurora system was used for analysis. Unsupervised clustering algorithms such as UMAP (Uniform Manifold Approximation and Projection for Dimension Reduction) and FlowSOM (flow cytometry data that builds self-organizing maps) were used in FlowJo to reveal the subpopulations of human APS related PBMCs. Populations were identified such as CD4+ helper T-cells, CD8+ cytotoxic T-cells, CD4+ regulatory T-cells, naive CD4+ or CD8+ T-cells, activated CD4+ or CD8+ T-cells, central memory CD4+ or CD8+ T-cells, terminal effector CD4+ or CD8+ T-cells, intermediate or early effector CD8+ T-cells, terminal effector CD8+ T-cells, γ/δ T-cells, naive or memory B-cells, NK cells, NKT cells, basophil granulocytes, monocytoid or plasmatocytoid dendritic cells, innate lymphoid cells, classic or non-classic monocytes, intermediate monocytes.

Results: The CD3+ TCRγ/δ -pan T-cell number was the lowest in APS-I gr., in contrast the CD4-CD8- T-cells were in the highest prevalence in that APS-I group. The frequency of CD4+ helper T-cells was the lowest in the APS-III gr., but the CD8+ cytoxic T-cells were in the highest rate in that APS-III cohort. Early effector CD8+ T-cells were decreased in both APS-I, -II, and-III groups compared to healthy controls.

Conclusion: The applicability of spectral FACS for the monitoring of the APS associated immunophenotype was shown in our study. The significant differences in T cell population among APS groups may raise the role of these cells in the pathomechanism of APS. Financing: FK142877 FK22, grant from the National Research, Development, and Innovation Office (NKFI), Hungary.

REFERENCES: NIL.

Acknowledgements: NIL.

Disclosure of Interests: None declared.

© The Authors 2025. This abstract is an open access article published in Annals of Rheumatic Diseases under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ). Neither EULAR nor the publisher make any representation as to the accuracy of the content. The authors are solely responsible for the content in their abstract including accuracy of the facts, statements, results, conclusion, citing resources etc.