Objective SLE is characterized by great clinical heterogeneity. Its complex pathogenesis has not been fully understood and factors influencing the development of different clinical phenotypes are still to unveil. IL-10 has dual effects, inhibiting pro-inflammatory cytokines while stimulating B-cell growth. In active SLE, there’s an elevated frequency of extrafollicular CCR6+ B-Helper T-cells among CD4+ T-cells, producing IL-10 and spontaneously inducing IgG, including pathogenic anti-dsDNA autoantibodies. Our study aimed to investigate the role of IL-10-secreting cells in Systemic Lupus Erythematosus (SLE) pathogenesis, exploring differences in their expression across disease stages and clinical phenotypes.

Methods Patients with a diagnosis of SLE according to 2019 classification criteria were enrolled. Inclusion criteria were active disease (SLEDAI-2k score ≥4) and/or early SLE (disease duration <12 months). Whole blood for peripheral mononuclear cells isolation was obtained from all patients. IL-10 expression in different cell subtypes was analyzed by flow cytometer using an anti-human IL-10 monoclonal antibody associated with specific lineage markers.

Results We looked at the percentage frequency of IL-10 -producing cells out of total lymphocytes under two conditions: ex vivo and after stimulation with PMA and ionomycin. 4 patients had high levels of IL-10 production ex vivo, while the remaining patients produced IL-10 only following stimulation as expected. We then divided the test population into two groups according to disease activity: patients with SLEDAI ≥ 4 displayed significantly higher IL-10 levels than inactive patients. To assess which cells were responsible for IL-10 production, we analyzed the percentage of CD4 and CD8 cells in two populations of lymphocytes, those that expressed IL-10 and those that did not. Spontaneously IL-10 secreting cells were mainly CD4+ helper T-cells expressing high levels of CCR6, CXCR5 and IL-7R.

Conclusions We demonstrate that IL-10 levels correlate with disease activity, accordingly to other studies. The role of IL-10 would be to stimulate autoreactive clones of B cells to produce pathogenic autoantibodies: the ex vivo production of IL-10 by B-helper T-cells in selected patients suggests that they are activated by autoantigens and contribute to the aberrant production of autoantibodies; however, further analysis will be needed to better characterize the spontaneously IL-10 producing lymphocytes.