Human CalDAG-GEFI deficiency increases bleeding and delays αIIbß3 activation.

Affinity regulation of integrin αIIbß3 for fibrinogen by inside-out signaling plays a critical role in hemostasis. Calcium and diacylglycerol (DAG)-regulated guanine nucleotide exchange factor I (CalDAG-GEFI) was identified as a Rap1-activating molecule, and its role in inside-out αIIbß3 activation was established in CalDAG-GEFI-deficient mice. However, little information regarding CalDAG-GEFI in human platelets is available. Here, we report a 16-year-old girl with CalDAG-GEFI deficiency who has been suffering from severe bleeding tendency. Although talin and kindlin-3 were normally detected, CalDAG-GEFI was undetectable in her platelets by western blotting. Genetic analysis revealed compound heterozygous CalDAG-GEFI mutations, Lys309X and Leu360del, which were responsible for CalDAG-GEFI deficiency. The functional analysis demonstrated impaired αIIbß3 activation by various agonists except for phorbol myristate acetate, normal calcium mobilization, and impaired Rap1 activation, which were consistent with the phenotype of CalDAG-GEFI-deficient mice. Despite substantial αIIbß3 activation at high agonist concentrations, she had severe bleeding tendency. Further functional analysis demonstrated markedly delayed αIIbß3 activation velocity and decreased shear-induced thrombus formation. Contrary to CalDAG-GEFI-deficient mice, which showed integrin-dependent neutrophil functional abnormality, neutrophil ß2 integrin activation was not impaired in the patient. Our results demonstrate the critical role of CalDAG-GEFI in rapid αIIbß3 activation of human platelets.

STI571 inhibits growth and adhesion of human mast cells in culture.

Stem cell factor (SCF)/c-kit system is critical for human mast cell development. We thus examined the effects of STI571, an inhibitor of the c-kit tyrosine kinase receptor, on the proliferation and function of human mast cells. STI571 at concentrations of 10(-6) M or higher almost completely abolished the SCF-dependent progeny generation from cord blood-derived cultured mast cells through an inhibition of the tyrosine phosphorylation of c-kit. The compound also suppressed the early phase of mast cell development. The extinction of mast cell growth induced by STI571 may be due largely to apoptosis according to the flow cytometric analysis and gel electrophoresis. Two-hour exposure to STI571 that failed to influence the total viable cell number suppressed adhesion of the cells to fibronectin in the presence of SCF without altering the expressions of integrin molecules. Our results may provide a fundamental insight for the clinical application of STI571 in allergic disorders.

Specific autoantibodies to platelet glycoproteins in Epstein-Barr virus-associated immune thrombocytopenia.

In this study, we detected autoantibodies to platelet glycoproteins GPIIb/IIIa and GPIb/IX on platelets and in plasma in a patient with immune thrombocytopenia associated with Epstein-Barr virus-related infectious mononucleosis. In addition, we present our findings on the effectiveness of intravenous immunoglobulin therapy for immune thrombocytopenia associated with Epstein-Barr virus.

Late-onset cases of familial hemophagocytic lymphohistiocytosis with missense perforin gene mutations.

Since the discovery of perforin gene mutations in familial hemophagocytic lymphohistiocytosis (FHL) type 2, heterogeneous features in FHL2 patients have been identified in a report of Feldmann et al. as the beginning. This study was conducted to determine the impact of characteristic gene mutations on late-onset (age > or = 7 years) hemophagocytic lymphohistiocytosis episodes. We analyzed perforin gene mutations in three late-onset cases from our registry in Japan and an additional 10 cases from the literature. Of the 13 cases with onset ages of a median of 10 (range 7-49) years, nine had homozygous and four had compound heterozygous missense mutations of the perforin gene. None had homozygous nonsense mutations. Our data suggest that nonsense perforin gene mutations yield early onset and missense mutations late onset in FHL2 cases.