Pathogenic Effects of Anti-Glycoprotein Ib Antibodies on Megakaryocytes and Platelets

Antibodies directed against the glycoprotein (GP) Ib have been identified as the potential cause of various platelet disorders: Immune thrombocytopenic purpura (ITP) may be caused by such autoantibodies; Anti-thrombotic drugs targeting GPIb also induce thrombocytopenia. In order to elucidate the potential mechanism(s) of the anti-GPIb effects, we have examined by electron microscopy (EM) the effect of several antibodies directed against GPIb and GPIIb-IIIa on human culture megakaryocytes (MK). Virtually all antibodies to GPIb enhanced the interaction of newly formed platelets with MK when compared to other antibodies. These effects were retrieved when antibodies were tested on platelets. We conclude that antibodies to GPIb can potentially inhibit platelet release by MK, and can also induce homotypic platelet adhesion. These results may have implications in the pathophysiology of thrombocytopenia and platelet recovery in ITP, and shed light on the pathological effect of anti-GPIb antibodies used as antithrombotic drugs.

Studies of alpha-granule proteins in cultured human megakaryocytes

alpha-Granule protein storage is important for producing platelets with normal haemostatic function. The low to undetectable levels of several megakaryocyte-synthesized alpha-granule proteins in normal plasma suggest megakaryocytes are important to sequester these proteins in vivo. alpha-Granule protein storage in vitro has been studied using other cell types, with differences observed in how some proteins are processed compared to platelets. Human megakaryocytes, cultured from cord blood CD34(+) cells and grown in serum-free media containing thrombopoietin, were investigated to determine if they could be used as a model for studying normal alpha-granule protein processing and storage. ELISA indicated that cultured megakaryocytes contained the alpha-granule proteins multimerin, von Willebrand factor, thrombospondin-1, beta-thromboglobulin and platelet factor 4, but no detectable fibrinogen and factor V. A significant proportion of the alpha-granule protein in megakaryocyte cultures was contained within the cells (averages: 41-71 %), consistent with storage. Detailed analyses of multimerin and von Willebrand factor confirmed that alpha-granule proteins were processed to mature forms and were predominantly located in the alpha-granules of cultured megakaryocytes.Thrombopoietin-stimulated cultured megakaryocytes provide a useful model for studying alpha-granule protein processing and storage.

HIV antibody screening remains indispensable for ensuring viral safety of blood components despite NAT implementation

BACKGROUND

The main objective of the implementation of NAT for the screening of blood-borne viruses was to compensate for the failure of serologic assays during the window period. Because this new screening procedure theoretically covers the entire period of infectivity, the necessity for maintaining serologic assays in blood screening strategy could become questionable.

STUDY DESIGN AND METHODS

To investigate this issue, a panel of 35 samples has been studied by NAT. These samples had been collected from HIV-1 antibody-positive individuals presenting a persistently low viral RNA load (<400 copies/mL) in the absence of antiviral therapy. All samples were analyzed with the minipool (x8) NAT routinely used in blood bank setting (HIV-1 and HCV assay based on transcription-mediated amplification) and with single-donation testing.

RESULTS

The minipool NAT failed to detect the presence of HIV RNA in 15 of the 35 samples (11 remained negative when retested). Single-donation testing gave negative results in 4 samples (3 remained negative when retested). Fourteen of the 18 samples with a viral load greater than 50 copies per mL were positive by minipool NAT versus 6 of the 17 samples with fewer than 50 copies per mL (p = 0.02).

CONCLUSION

The results clearly demonstrate that anti-HIV screening should not be withdrawn from biologic qualification procedures of blood donations, even when single NAT is performed.

Pathogenic effects of anti-glycoprotein Ib antibodies on megakaryocytes and platelets

Antibodies directed against the glycoprotein (GP) Ib have been identified as the potential cause of various platelet disorders: Immune thrombocytopenic purpura (ITP) may be caused by such autoantibodies; Anti-thrombotic drugs targeting GPIb also induce thrombocytopenia. In order to elucidate the potential mechanism(s) of the anti-GPIb effects, we have examined by electron microscopy (EM) the effect of several antibodies directed against GPIb and GPIIb-IIIa on human culture megakaryocytes (MK). Virtually all antibodies to GPIb enhanced the interaction of newly formed platelets with MK when compared to other antibodies. These effects were retrieved when antibodies were tested on platelets. We conclude that antibodies to GPIb can potentially inhibit platelet release by MK, and can also induce homotypic platelet adhesion. These results may have implications in the pathophysiology of thrombocytopenia and platelet recovery in ITP, and shed light on the pathological effect of anti-GPIb antibodies used as antithrombotic drugs.

[Relevance of cytological and immunophenotypical analysis for the diagnosis of B-cell chronic lymphocytic leukaemia]

The objective of this study was to describe the cytological and immunophenotypical parameters evocative of B-cell Chronic Lymphocytic Leukaemia (B-CLL) and their ability to participate to the differential diagnosis of other B-chronic lymphoproliferatives disorders with blood dissemination (B-CLD). Two groups of pathology included 92 patients, 79 patients had a B-CLL and the 13 other had a B-CLD (1 Prolymphocytic Leukaemia, 12 non- Hodgkin's Lymphoma in which 4 Splenic Lymphoma with Villous Lymphocytes or SLVL). The lymphoid morphology was studied on blood smear stained with May Gr nwald Giemsa and the immunophenotypical analysis was performed by flow cytometry. The 72 patients with B-CLL were characterized by a predominance of small mature lymphocytes with a Matutes's CLL score 3 (generally CD5+, CD23+, SmIg poor expression). 4 out of B-CLL with cleaved lymphocytes 5 % showed the same immunological characteristics than the typical B-CLL cases. 3 cases of B-CLL with prolymphocytes between 5 and 55 % showed in 2 cases an immunophenotyping compatible with the diagnosis of B-CLD. The presence of shadow cells of Gumprecht was highly evocative of B-CLL. In conclusion, the cytological analysis remains at the root of any diagnosis and can be sufficient in most cases of typical CLL with the presence of shadow cells of Gumprecht on the blood smear. In case of presence of cleaved lymphocytes, the immunophenotyping becomes essential to confirme the diagnosis of B-CLL. In prolymphocytic cases, the differential diagnosis between mixed CLL and B-CLD (especially Mantle Cell Lymphoma and Marginal Zone B-Cell Lymphoma without villous lymphocytes) needs a multidisciplinary approach (clinical, cytogenetical and histological).

Oxidized LDL activates STAT1 and STAT3 transcription factors: possible involvement of reactive oxygen species

The effect of cupric ion-oxidized low density lipoprotein (Cu-LDL) or endothelial cell-oxidized LDL (E-LDL) on STAT1 and STAT3 (signal transducers and activators of transcription) DNA binding activity was investigated by electrophoretic mobility shift assay in human endothelial cells. Both oxidized LDL enhanced STAT1 and STAT3 binding to their respective consensus binding sites. Furthermore, the activation of STATs was proportional to the oxidation degree of LDL in that the highly oxidized Cu-LDL exhibited a more marked effect than E-LDL. Oxidized LDL induced an intracellular oxidative stress, as shown by the increase in the intracellular level of lipid peroxidation products (thiobarbituric acid-reactive substances) and in the level of reactive oxygen species, measured by the fluorescence of dichlorofluorescein diacetate. The binding activity of STAT1 and STAT3 paralleled these two parameters, which suggests that it is dependent upon the redox state of the cell. The activation of STATs by oxidized LDL was almost completely inhibited by the lipophilic antioxidant vitamin E, and partially antagonized by the hydrophilic thiol-containing compound N-acetylcysteine, suggesting that the oxidative stress induced by oxidized LDL is involved in the observed phenomenon. Furthermore, the lipid extract of Cu-LDL also activated STAT1 and STAT3. Since the STAT pathway plays a key role in cytokine and growth factor signal transduction, the activation of STATs by oxidized LDL might be related to their proinflammatory and fibroproliferative effect in the atherosclerotic plaque.