RESUMO
B lymphocytes producing antiplatelet autoantibodies play a major role in autoimmune thrombocytopenia (ITP). However, certain B cells, including the human CD19(+)CD24(hi)CD38(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(hi)CD38(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(hi)CD38(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.
Assuntos
Apresentação de Antígeno/imunologia , Linfócitos B Reguladores/imunologia , Monócitos/imunologia , Púrpura Trombocitopênica Idiopática/imunologia , Adolescente , Adulto , Idoso , Idoso de 80 Anos ou mais , Antígenos CD/metabolismo , Linfócitos B Reguladores/metabolismo , Plaquetas/imunologia , Estudos de Casos e Controles , Células Cultivadas , Feminino , Citometria de Fluxo , Humanos , Interleucina-10/metabolismo , Masculino , Pessoa de Meia-Idade , Monócitos/metabolismo , Púrpura Trombocitopênica Idiopática/metabolismo , Adulto JovemRESUMO
Platelet survival depends upon mediators of apoptosis e.g., Bcl-xL, Bax, and Bak, which are regulated by thrombopoietin (TPO)-mediated AKT signaling. Thrombopoietin receptor (TPO-R) signaling might decrease platelet and/or megakaryocyte apoptosis and increase the platelet count. This study therefore explored anti-apoptotic effects of TPO-R-agonists in vivo on platelets of patients with immune thrombocytopenia. Patients received eltrombopag or romiplostim for two weeks. Total, immature, and large platelet counts were assessed as were Bcl-xL inhibitor assay; Bcl-xL Western blot; and flow cytometric (FACS) analysis of the AKT-signaling pathway. Eight/ten patients had platelet responses to eltrombopag and all three to romiplostim. Platelet sensitivity to apoptosis by Bcl-xL inhibition was greater in pretreatment patients than controls. This sensitivity normalized after one week of therapy, but surprisingly returned to pretreatment levels at week two. FACS analysis revealed increased AKT-pathway signaling after one week, followed by a decrease at week two. Platelet counts correlated with the Bcl-xL /Bak ratio. Platelet survival may be enhanced by TPO-R-agonists as a transient decrease in platelet sensitivity to apoptosis was accompanied by transient activation of AKT. However, this mechanism has only a short-lived effect. Megakaryocytes and platelets already present at the start of TPO-R-agonist treatment appear to respond differently than those generated de novo.
Assuntos
Benzoatos/uso terapêutico , Plaquetas/efeitos dos fármacos , Hidrazinas/uso terapêutico , Megacariócitos/efeitos dos fármacos , Púrpura Trombocitopênica Idiopática/tratamento farmacológico , Pirazóis/uso terapêutico , Receptores Fc/uso terapêutico , Receptores de Trombopoetina/agonistas , Proteínas Recombinantes de Fusão/uso terapêutico , Trombopoetina/uso terapêutico , Apoptose/efeitos dos fármacos , Apoptose/genética , Plaquetas/metabolismo , Plaquetas/patologia , Estudos de Casos e Controles , Doença Crônica , Regulação da Expressão Gênica , Humanos , Megacariócitos/metabolismo , Megacariócitos/patologia , Púrpura Trombocitopênica Idiopática/genética , Púrpura Trombocitopênica Idiopática/metabolismo , Púrpura Trombocitopênica Idiopática/patologia , Receptores de Trombopoetina/genética , Receptores de Trombopoetina/metabolismo , Transdução de Sinais , Proteína Killer-Antagonista Homóloga a bcl-2/genética , Proteína Killer-Antagonista Homóloga a bcl-2/metabolismo , Proteína X Associada a bcl-2/genética , Proteína X Associada a bcl-2/metabolismo , Proteína bcl-X/genética , Proteína bcl-X/metabolismoRESUMO
Immune thrombocytopenia (ITP) is an autoantibody-mediated bleeding disorder with both accelerated platelet destruction and impaired platelet production. We and others have described impaired regulatory CD4(+)CD25(hi) T cells (Treg) numbers and/or suppressive function in ITP patients. Clinical trials using thrombopoietic agents to stimulate platelet production have shown favorable outcomes in ITP patients, but information on the immunologic responses of treated patients are lacking. We studied the immunologic profile of chronic ITP patients before (n = 10) and during treatment with thrombopoietin receptor (TPO-R) agonists (n = 9). Treg activity, as measured by suppression of proliferation of autologous CD4(+) CD25(-) cells, was improved in patients on treatment (P < .05), and the improvement correlated with reduction in interleukin-2-producing CD4(+) cells, consistent with dampening of immune responses. There was a concomitant increase in total circulating transforming growth factor-ß1 (TGF-ß1) levels (P = .002) in patients on treatment, and the levels of TGF-ß1 correlated with the degree of improvement in platelet counts (r = .8, P = .0002). This suggests that platelets in patients on TPO-R treatment may play a role in improving Treg function, either directly or indirectly by enhanced release of TGF-ß1 as a result of greater platelet turnover. In conclusion, our findings suggest that thrombopoietic agents in patients with ITP have profound effects to restore immune tolerance.