PO:15:218 | Evaluation of leukocyte expression of ecto-nucleotidase in patients with systemic lupus erythematosus

Background. Ecto-nucleotidases are membrane proteins that modulate the immune response through the extracellular conversion of pro-inflammatory mediators ATP and NAD into adenosine, a molecule with immunosuppressive functions. These enzymatic reactions are mediated by ectonucleotidases CD39 and CD73 and, to a lesser extent, by CD38, CD157, CD203a and CD203c. In systemic lupus erythematosus (SLE), alterations in serum ATP levels and adenosine receptors suggest a dysregulation of these pathways. Therefore, the aim of the study was to characterise the expression of ectonucleotidases in B and T lymphocytes, natural killer (NK) cells and dendritic cells (DCs) of patients with SLE, evaluating the association with disease activity status.   Methods. Consecutive patients diagnosed with SLE according to the 2019 EULAR/ACR criteria and healthy controls matched for age and sex were enrolled. Clinical-demographic data were collected and peripheral blood mononuclear cell samples were collected and analysed by spectral flow cytometry for the detection of CD39, CD73, CD38, CD157, CD203a and CD203c. Patients were stratified according to disease remission status according to the DORIS definition.   Results. The study included 57 SLE patients with a female-to-male ratio of 10:1 and a median age of 45 years (Table 1). Compared to controls, patients had reduced expression of CD73 in naïve B lymphocytes and cytotoxic T lymphocytes (Figure 1 A/B). Overall, there was increased expression of CD157, CD38, CD203a, and CD203c in mature B lymphocytes, T helper lymphocytes, DCs, and NK cells. In addition, there was an increase in CD39+ and CD73+ in NK cells, while the proportion of CD39+ was increased in DCs. In patients in remission according to the DORIS definition, an increase in CD39+ Treg cells was observed compared to those who did not achieve remission (Figure 1 C).   Conclusions. This study is the first to conduct a comprehensive analysis of the expression of ecto-nucleotidases in different leukocyte populations of patients with SLE. Significantly, a reduction in the expression of CD73, an enzyme essential for the synthesis of extracellular adenosine, was found in the naïve B lymphocytes and cytotoxic T lymphocytes of patients. Since adenosine exerts an immunosuppressive action, the reduction in its peri-cellular concentration could promote the activation of these lymphocyte populations. Conversely, several cell types showed increased expression of ectonucleotidases. Since the expression of these enzymes is induced by various pro-inflammatory cytokines, this phenomenon could constitute a compensatory mechanism aimed at reducing excessive concentrations of the pro-inflammatory mediators ATP and NAD. Patients in remission according to the DORIS definition showed an increase in CD39+ Tregs, cells that exert an immunosuppressive action by depleting extracellular ATP, suggesting a possible role for these cells in disease remission.