Transient and chronic childhood immune thrombocytopenia are distinctly affected by Fc-γ receptor polymorphisms.

In childhood immune thrombocytopenia (ITP), anti-platelet autoantibodies mediate platelet clearance through Fc-γ receptor (FcγR)-bearing phagocytes. In 75% to 90% of patients, the disease has a transient, self-limiting character. Here we characterized how polymorphisms of FcγR genes affect disease susceptibility, response to intravenous immunoglobulin (IVIg) treatment, and long-term recovery from childhood ITP. Genotyping of the FCGR2/3 locus was performed in 180 children with newly diagnosed ITP, 22 children with chronic ITP, and 180 healthy control children by multiplex ligation-dependent probe amplification. Children with newly diagnosed ITP were randomly assigned to a single administration of IVIg or observation, and followed for 1 year (Treatment With or Without IVIg for Kids With ITP [TIKI] trial). We defined transient ITP as a complete recovery (≥100 × 109/L) 3 months after diagnosis, including both self-limiting disease/IVIg responders and chronic ITP as absence of a complete recovery at 12 months. ITP susceptibility, as well as spontaneous recovery and response to IVIg, was associated with the genetic variants FCGR2C*ORF and FCGR2A*27W and the FCGR2B promoter variant 2B.4. These variants were overrepresented in patients with transient (N = 131), but not chronic (N = 43), disease. The presence of FCGR2C*ORF predisposed to transient ITP with an odds ratio of 4.7 (95% confidence interval, 1.9-14.3). Chronic ITP was associated with a deletion of FCGR2C/FCGR3B (copy number region 1) with an odds ratio of 6.2 (95% confidence interval, 1.8-24.7). Taken together, susceptibility to transient and chronic ITP is distinctly affected by polymorphic variants of FCGR2/3 genes. Our data suggest that genotyping of the FCGR2/3 locus may be useful for prognosis and guidance of treatment decisions in newly diagnosed childhood ITP.

Intravenous immunoglobulin vs observation in childhood immune thrombocytopenia: a randomized controlled trial.

Management of children with newly diagnosed immune thrombocytopenia (ITP) consists of careful observation or immunomodulatory treatment. Observational studies suggest a lower risk for chronic ITP in children after intravenous immunoglobulin (IVIg) treatment. In this multicenter randomized trial, children aged 3 months to 16 years with newly diagnosed ITP, platelet counts 20 × 109/L or less, and mild to moderate bleeding were randomly assigned to receive either a single infusion of 0.8 g/kg IVIg or careful observation. Primary outcome was development of chronic ITP, which at the time of study initiation was defined as a platelet count lower than 150 × 109/L after 6 months. Two hundred six children were allocated to receive IVIg (n = 102) or careful observation (n = 104). Chronic ITP occurred in 18.6% of the patients in the IVIg group and 28.9% in the observation group (relative risk [RR], 0.64; 95% confidence interval [CI], 0.38-1.08). Platelet counts lower than 100 × 109/L at 12 months (current definition of chronic ITP) were observed in 10% of children in the IVIg group and 12% in the observation group (RR, 0.83; 95% CI, 0.38-1.84). Complete response rates in the first 3 months were significantly higher in the IVIg group. Immunoglobulin G Fc receptor IIb genetic variations were associated with early complete response in both groups. Grade 4 to 5 bleeding occurred in 9% of the patients in the observation group vs 1% in the IVIg group. This trial was registered at www.trialregister.nl as NTR 1563.

Functional platelet defects in children with severe chronic ITP as tested with 2 novel assays applicable for low platelet counts.

Immune thrombocytopenia (ITP) is an autoimmune disease with a complex heterogeneous pathogenesis and a bleeding phenotype that is not necessarily correlated to platelet count. In this study, the platelet function was assessed in a well-defined cohort of 33 pediatric chronic ITP patients. Because regular platelet function test cannot be performed in patients with low platelet counts, 2 new assays were developed to determine platelet function: first, the microaggregation test, measuring in platelets isolated from 10 mL of whole blood the platelet potential to form microaggregates in response to an agonist; second, the platelet reactivity assay, measuring platelet reactivity to adenosine diphosphate (ADP), convulxin (CVX), and thrombin receptor activator peptide in only 150 µL of unprocessed whole blood. Patients with a severe bleeding phenotype demonstrated a decreased aggregation potential upon phorbol myristate acetate stimulation, decreased platelet degranulation following ADP stimulation, and a higher concentration of ADP and CVX needed to activate the glycoprotein IIbIIIa complex compared with patients with a mild bleeding phenotype. In conclusion, here we have established 2 functional tests that allow for evaluation of platelet function in patients with extremely low platelet counts (<10(9)). These tests show that platelet function is related to bleeding phenotype in chronic ITP.

p38 MAP kinase inhibits neutrophil development through phosphorylation of C/EBPalpha on serine 21.

Many extracellular stimuli regulate growth, survival, and differentiation responses through activation of the dual specificity mitogen activated protein kinase (MAPK) kinase three (MKK3) and its downstream effector p38 MAPK. Using CD34+ hematopoietic progenitor cells, here we describe a novel role for MKK3-p38MAPK in the regulation of myelopoiesis. Inhibition of p38MAPK utilizing the pharmacological inhibitor SB203580, enhanced neutrophil development ex vivo, but conversely reduced eosinophil differentiation. In contrast, constitutive activation of MKK3 dramatically inhibited neutrophil differentiation. Transplantation of beta2-microglobulin(-/-) nonobese diabetic/severe combined immune deficient (NOD/SCID) mice with CD34+ cells ectopically expressing constitutively active MKK3 resulted in reduced neutrophil differentiation in vivo, whereas eosinophil development was enhanced. Inhibitory phosphorylation of CCAAT/enhancer binding protein alpha (C/EBPalpha) on serine 21 was induced upon activation of p38MAPK. Moreover, ectopic expression of a non-phosphorylatable C/EBPalpha mutant was sufficient to abrogate MKK3-induced inhibition of neutrophil development. Furthermore, treatment of CD34+ progenitors from patients with severe congenital neutropenia with SB203580 restored neutrophil development. These results establish a novel role for MKK3-p38MAPK in the regulation of lineage choices during myelopoiesis through modulation of C/EBPalpha activity. This signaling module may thus provide an important therapeutic target in the treatment of bone marrow failure.