This study aims to investigate the molecular mechanism of bleeding in patients with Systemic Lupus Erythematosus (SLE) complicated by Immune Thrombocytopenia (ITP), to clarify the differential expression of monocyte-derived exosomal miR-155 between bleeding patients and those without bleeding symptoms, and to evaluate the relationship between this molecule and SLE disease activity, thereby providing new insights for the treatment of bleeding in SLE complicated by ITP.

1.     Clinical Sample Collection: Patients with SLE and ITP were enrolled and divided into a bleeding group and a non-bleeding group based on the presence of bleeding symptoms (10 cases per group). The diagnosis of SLE adhered to the 2019 EULAR/ACR SLE classification criteria. The diagnosis of immune thrombocytopenia followed traditional criteria: peripheral blood platelet count < 100×10^9^/L, normal or increased megakaryocytes on bone marrow aspiration, and exclusion of other conditions that can cause immune-mediated platelet reduction, such as HIV, lymphoproliferative disorders, thyroid diseases, and liver diseases. Disease activity was assessed using the SLEDAI score. Bleeding symptoms were defined as: purpura (petechial skin hemorrhages) caused by thrombocytopenia, or bleeding caused by vascular wall necrosis due to vasculitis, excluding bleeding resulting from trauma, medications (e.g., anticoagulants), or menstrual factors.

2.     Experimental Procedures: Peripheral blood was collected, and monocytes were isolated. Plasma exosomes were isolated using ultracentrifugation. Exosomal markers (CD81, TSG101, ALIX) were detected by Western blot. The expression levels of miR-155 in exosomes and monocyte supernatant were detected by qPCR, and their correlation with bleeding severity and disease activity indicators was analyzed.

The expression of miR-155 in peripheral blood monocyte-derived exosomes was significantly higher in the bleeding group compared to the non-bleeding group and was positively correlated with bleeding severity and disease activity.

The expression of monocyte-derived exosomal miR-155 is significantly elevated in SLE patients with thrombocytopenia and may be involved in the crucial mechanism of bleeding in SLE patients complicated with ITP. Targeted intervention against miR-155 or exosomes could provide new therapeutic strategies for this complication.