Neutrophils contribute to elevated BAFF levels to modulate adaptive immunity in patients with primary immune thrombocytopenia by CD62P and PSGL1 interaction

OBJECTIVES: Immune thrombocytopenia (ITP) is an autoimmune disease characterised by impaired platelet production and increased platelet destruction. However, the involvement of neutrophils in ITP is yet to be explored. METHODS: B‐cell activating factor (BAFF) expression and activation markers of neutrophils, as well as activation of platelets in ITP patients and healthy controls were measured. The interaction of CD62P on platelets and BAFF in neutrophils was analysed by correlation analysis and verified by co‐culture. The effects of neutrophils on apoptosis of acquired immune cells were evaluated in co‐culture systems with or without belimumab. RESULTS: The BAFF expression and activation of neutrophils were increased in active ITP patients. BAFF levels in neutrophils were positively correlated with CD62P(+) platelets and neutrophils produced increased BAFF by interfering with CD62P on platelets. Neutrophils inhibited the apoptosis of CD4(+), CD8(+) and CD19(+) cells dependent on BAFF levels, and belimumab could interrupt the effects of neutrophils. CONCLUSIONS: Neutrophils were overactivated in ITP patients and participated in the progression of disease by producing excessive BAFF, which could be regulated by CD62P on platelets. Targeting BAFF by belimumab may be a novel potential therapy for ITP.