A novel method for the assessment of pro- and anti-coagulant properties of platelet-derived microvesicles and its usefulness for quality monitoring of platelet haemostatic function.

To investigate the pro- and anti-coagulant properties of platelet-derived microvesicle (MV), a novel procedure for the removal of plasma proteins was designed, which allows determination of these activities in a purified system in the same reaction vessel. While the pro-coagulant activity of the isolated MV increased on day 5 as compared to day 1, the anti-coagulant activity was significantly reduced.     

Clamp loading,unloading and intrinsic stability of the PCNA, β and gp45 sliding clamps of human,E. coli and T4 replicases

Background: The high speed and processivity of replicative DNA polymerases reside in a processivity factor which has been shown to be a ring-shaped protein. This protein (‘sliding clamp’) encircles DNA and tethers the catalytic unit to the template. Although in eukaryotic, prokaryotic and bacteriophage-T4 systems, the processivity factors are ring-shaped, they assume different oligomeric states. The Escherichia coli clamp (the β subunit) is active as a dimer while the eukaryotic and T4 phage clamps (PCNA and gp45, respectively) are active as trimers. The clamp can not assemble itself on DNA. Instead, a protein complex known as a clamp loader utilizes ATP to assemble the ring around the primer-template. This study compares properties of the human PCNA clamp with those of E. coli and T4 phage. Results: The PCNA ring is a stable trimer down to a concentration below 100 nm (K_d ≈ 21 nm ). On DNA, the PCNA clamp slides freely and dissociates from DNA slowly (t_1/2 ≈ 24 min). β is more stable in solution (K_d < 60 pm ) and on DNA (t_1/2 ≈ 1 h) than PCNA which may be explained by its simpler oligomeric state. The T4 gp45 clamp is a much less stable trimer than PCNA (K_d ≈ 250 nm ) and requires association with the polymerase to stabilize it on DNA as observed previously. The consequence of this cooperation between clamp and polymerase is that upon finishing a template and dissociation of the polymerase from DNA, the gp45 clamp spontaneously dissociates from DNA without assistance. However, the greater stability of the PCNA and β clamps on DNA necessitates an active process for their removal. The clamp loaders (RF-C and γ complex) were also capable of unloading their respective clamps from DNA in the presence of ATP. Conclusions: The stability of the different clamps in solution correlates with their stability on DNA. Thus, the low stability of the T4 clamp explains the inability to isolate gp45 on DNA. The stability of the PCNA and β clamps predicts they will require an unloading factor to recycle them on and off DNA during replication. The clamp loaders of PCNA and β double as clamp unloaders presumably for the purpose of clamp recycling.     

Factual reflections and recommendations on extracorporeal photopheresis in pediatrics

One of the biggest challenges in evaluating available literature on extracorporeal photopheresis (ECP) practices in pediatric patients is the marked heterogeneity of approaches to the patient evaluation, procedural aspects and apheresis product analysis. These issues are most relevant in ECP management in children with graft versus host disease (GVHD) after hematopoietic stem cell transplantation. Extracorporeal photopheresis in pediatric patients is considered relatively safe with few adverse effects reported from retrospective or observational studies. Careful patient eligibility assessment for ECP procedures and close monitoring while on ECP therapy is still required by transfusion medicine and pediatric specialists. Particular attention is necessary considering the rapidly changing clinical status of children with graft versus host disease after hematopoietic stem cell transplantation, focusing on hemodynamic compromise, hematologic and metabolic disturbances. This is a review of the approaches to some of the safety issues in long-term ECP therapy in low-weight pediatric patients.     

Are All Leucodepleted Platelet Concentrates Equivalent?

BACKGROUND AND OBJECTIVES: A number of technologies are available for the production of leucocyte-depleted platelet concentrates (PCs). This study compared the characteristics of PCs prepared by three commonly used techniques. MATERIALS AND METHODS: In total, fifteen units of leucocyte-depleted PCs prepared by the Cobe LRS Turbo apheresis system, Haemonetics MCS+ with in-line filter and filtration of PCs derived from pooled buffy coats (BCs) were transferred into the same standard container. Markers to assess status/activation and microvesiculation of platelets as well as platelet injury were measured. RESULTS: pH was well maintained in all types of PCs. The expression of CD62P was higher in Cobe LRS Turbo on day 1 but became equivalent between the three methods on day 5. A significant correlation was found between the expression of CD62P on platelet surface and soluble CD62P in the plasma. The degree of phosphatidylserine (PS) exposure was slightly higher in Cobe LRS Turbo and BC-PCs than Haemonetics MCS+ on day 1. However, on day 5 both apheresis PC values were higher than BC-PCs. A significant correlation was found between PS exposure and microvesiculation. CONCLUSION: Leucodepleted PCs prepared by the three methods were different in terms of storage lesion and microvesiculation. The clinical significance of these findings remains to be investigated.     

Red cell transfusion in paediatric patients with thalassaemia and sickle cell disease: Current status,challenges and perspectives

Notwithstanding the high safety level of the currently available blood for transfusion and the decreasing frequency of transfusion-related complications, administration of labile blood products to paediatric patients still poses unique challenges and considerations. The incidence of thalassaemia and sickle cell disease in the paediatric population may be high enough under specific racial and geographical contexts. Red cell transfusion is the cornerstone of β-thalassaemia treatment and one of the most effective ways to prevent or correct specific acute and chronic complications of sickle cell disease. However, this life-saving strategy comes with its own complications, such as additional iron overload, alloimmunization and haemolytic reactions, among others. In paediatrics, the dependency of the transfusion outcome upon disease and other recipient characteristics is more prominent compared with the adults, owing to differences in developmental maturity and physiology that render them more susceptible to common risks, exacerbate the host response to transfused cells, and modify the type or the clinical severity of the transfusion-related morbidity. The adverse branch of red cell transfusion is likely the overall effect of several factors acting synergistically to shape the clinical phenotype of this therapy, including inherent donor/blood unit variables, like antigenicity, red cell deformability and extracellular vesicles, as well as recipient variables, such as history of alloimmunization and inflammation level at time of transfusion. This review focuses on paediatric patients with β-thalassaemia and sickle cell disease as a recipient group with distinct transfusion-related characteristics, and introduces new concepts for consideration, not adequately studied and elucidated so far.