ANALYSIS OF THE EXPRESSION OF T-BET IN B LYMPHOCYTES OF PATIENTS WITH SYSTEMIC LUPUS ERYTHEMATOSUS

E. Marasco, G. M. Moneta, C. Bracaglia, I. Caiello, C. Farroni, R. Carsetti, F. De BenedettiBambino Gesu’ Children Hospital, Unit of Rheumatology, Rome, Italy Bambino Gesu’ Children Hospital, B Cell Physiopathology Unit, Rome, Italy  Background Systemic lupus erythematosus (SLE) is an autoimmune disease causing significant morbidity and mortality. B cells play a central role in SLE pathogenesis. T-bet, is a transcription factor promoting T helper-1 development. B cells expressing T-bet are expanded in aging, chronically infected individuals, and murine models of autoimmunity [1, 2]. Objectives The aim of our work is to analyze the expression and regulatory mechanisms of the transcription factor T-bet in B cells of patients with systemic lupus erythematosus (SLE). Methods The intracellular expression of T-bet was evaluated by flow cytometry in the different subsets of B lymphocytes of SLE patients and controls (HD). Peripheral blood mononuclear cells (PBMCs) were stimulated in vitro with IFNγ and IFNα and the expression of T-bet was evaluated by flow cytometry. The clinical characteristics of patients were analyzed by Multiple Factor Analysis (MFA). The analysis was carried out with the software R. Results We performed B cell staining and assessed the expression of T-bet in B cell subsets in patients with SLE and HD. We observed a significant expansion of naïve B cells and double negative (DN) B cells expressing T-bet in patients with SLE compared to HD (Figure 1A-B). An expansion of T-bet+ naïve B cells above the 99th percentile of HD (>1% of total naïve B cells) was evident in 68% of patients; 47% of patients showed an expansion of T-bet+ DN B cells above the 99th percentile of HD (>22% of total DN B cells). We assessed if patients with expanded T-bet+ naïve or DN B cells showed significant clinical differences from patients without the expanded subpopulations. To this end we collected clinical and laboratory parameters (SLEDAI, organ involvement as classified in the BILAG, damage with SDI, autoantibody profile, treatment and disease duration) and performed a multiple factor analysis (MFA). The aim of this analysis was to reduce the dimensionality of the complex data to few variables without losing information. The first 4 dimensions of MFA explained 58% of the total variance. The first dimension accounted for 23.6% of variance, and it was mostly driven by therapy and BILAG scores; the second dimension accounted for 17.7% of the variance and it was mostly driven by SLEDAI, SDI and serology. Patients with expanded T-bet+ naïve B cells, distributed differently from patients with no expansion of T-bet+ naïve B cells (Figure 1C). The first dimension was the most informative in separating the two groups of patients: significantly higher values were reported for patients with expanded T-bet+ naïve B cells. No differences were observed for patients with and without expanded T-bet+ DN B cells (Figure 1C). We investigated in vitro if the expression of T-bet in B cells was driven by interferons. We stimulated PBMCs of HD with IFNγ or IFNα and assessed the frequency of T-bet+ B cells: both interferons induced the expression of T-bet in naïve (CD19+CD27-) and memory (CD19+CD27+) B cells (Figure 1D). Interestingly, when cells were stimulated with IFNα in the presence of IFNγ-blocking antibodies the expression of T-bet was not induced. Conclusion Altogether, T-bet+ naïve B cells are expanded in patients with SLE and define a group of patients with clinically different disease from patients without expanded T-bet+ Naïve B cells. The expression of T-bet is induced specifically by IFNγ and not by IFNα. References Karnell JL, Cellular immunology 2017 Knox JJ, JCI insight 2017 Figure 1. Image/graph: Acknowledgements: NIL. Disclosure of Interests None Declared. Keywords: Systemic lupus erythematosus, Biomarkers, Cell biology DOI: 10.1136/annrheumdis-2023-eular.4537Citation: , volume 82, supplement 1, year 2023, page 1185Session: Adaptive immunity (T cells and B cells) in rheumatic diseases (Publication only)