Defective regulatory B-cell compartment in patients with immune thrombocytopenia

摘要

B lymphocytes producing antiplatelet autoantibodies play a major role in autoimmune thrombocytopenia (ITP). However, certain B cells, including the human CD19+CD24 hiCD38 hi subpopulation, possess regulatory functions mediated partly by IL-10. In a cohort of chronic ITP patients with low platelet counts who consisted of patients off treatment, we found a lower frequency of CD19 +CD24 hiCD38 hi in the peripheral compartment of nonsplenectomized patients (P =.03). IL-10 expression after activation was decreased in all ITP circulating CD19 + subpopulations (P .03), and inhibition of monocyte TNF-α expression by activated B cells was reduced in patients with platelet numbers of 50 × 10 9 cells/L (P =.001), indicating that regulatory B cells of patients with ITP are functionally impaired in their ability to dampen monocyte activation. Interestingly, in nonsplenectomized patients whose platelet counts were elevated after treatment with thrombopoietic agents, the frequency of CD19 +CD24 hiCD38 hi B cells was increased compared with those before treatment (P =.02). Altogether, these data indicate a compromised regulatory B-cell compartment as an additional defect in immune regulation in patients with chronic ITP that may be restored in responders to thrombopoietic treatment.