IL-2 detected by flow cytometry and its significance in systemic lupus erythematosus

Low-dose interleukin 2 (IL-2) administration has been shown to selectively modulate regulatory T (Treg) cell abundance and alleviate the progression of systemic lupus erythematosus (SLE). IL-2 level could be indicator of low-dose IL-2 usage in SLE patients. However, current methods for IL-2 detection are generally not sensitive to be used in clinic. This study aims to establish flow cytometry-based IL-2 detection as a feasible approach in determining IL-2 in peripheral blood of SLE patients.

Flow cytometry was used to quantify the relative mean fluorescence intensity (MFI) of IL-2 in CD3⁺T cells and other lymphocyte subsets in peripheral blood mononuclear cell (PBMCs) from a cohort of 134 SLE patients and 112 healthy controls (HC). Correlations between IL-2 MFI and clinical or laboratory parameters in SLE patients were also investigated.

MFI of IL-2 represented IL-2 expression in CD3⁺T cells. IL-2 MFI was significantly lower in SLE patients compared to the HC group and negatively associated with anti-ribosomal protein antibodies, erythrocyte sedimentation rate (ESR), and blood urea. Conversely, it was positively correlated with IgA and hemoglobin. These associations with IgA, hemoglobin, ESR, and blood urea remained significant after adjusting for age and disease duration. IL-2 level was also positively correlated with the relative abundance of Th1, Th2, and Th17 cells. Furthermore, MFI of IL-2 recovered with effective treatment in SLE patients.

MFI of IL-2 serves as a feasible marker of IL-2, which is significantly decreased in SLE patients and recovered with treatment, suggesting its potential for assessing short-term disease status and treatment response in SLE patients. Key Points • IL-2 MFI can be used to estimate IL-2 expression level in SLE patients.  • IL-2 MFI is significantly reduced in SLE patients. • IL-2 MFI can serve as a marker for monitoring SLE activity and short-term status.