A patient with autoimmune thrombocytopenic purpura demonstrating serum antibodies reactive with mouse cross-reactive idiotypes

Large-scale production, bacterial localization assessment and immobilized metal affinity chromatography purification of a human single-chain Fv antibody against alphaIIb-beta3 integrin

Our objective was to investigate the Escherichia coli localization (such as supernatant, cytoplasm and inclusion bodies) of an anti-alphaIIb-beta3 (alphaIIbbeta3) scFv fragment referred to as scFv[EBB3] produced in batch fermentation. Immobilized metal affinity chromatography (IMAC) purification was performed on supernatant using expanded bed absorbed technology (EBA) and on sonicated cells in native conditions over an immobilized copper-ion affinity column. Inclusion bodies were solubilized before IMAC purification and the refolding procedure was performed on the column. The majority of scFv[EBB3] were present as inclusion bodies (55%), whereas 36% were found in the cytoplasm and only 9% secreted in the supernatant. The scFv activity was assessed by enzyme-linked immunosorbent assay (ELISA), flow cytometry and immunohistochemistry analyses performed on a thrombus induced in vivo on an atherosclerotic rabbit model.

Analysis of the V genes coding for a monospecific human antibody to myosin and functional expression of single chain Fv fragments

A monospecific human IgM monoclonal antibody (mAb), reactive with myosin from human heart, has been obtained by EBV transformation. This mAb may have a diagnostic potential in the imaging of myocardial necrosis. However, owing to the fact that the molecular mass of an IgM is 900 kDa, a poor diffusion and a slow penetration inside necrotic myocytes could reduce its capacity for scintigraphic detection. In order to alleviate these problems, we constructed the scFv by cloning the VH and VL domains into the pHOG21 vector. Analysis of the V genes proved an unmutated configuration showing that the immortalized B cell issued from the primary IgM repertoire. The expression product in Escherichia coli was a 35 kDa scFv fragment with the antigen-binding specificity of the parental mAb.

Autoimmune thrombocytopenic purpura (AITP) and acquired thrombasthenia due to autoantibodies to GP IIb-IIIa in a patient with an unusual platelet membrane glycoprotein composition

The subject (E.B.) is a 63-year-old woman with autoimmune thrombocytopenic purpura (AITP) who was first examined some 6 years ago with symptoms of epistaxis and gum bleeding, severe thrombocytopenia, and large platelets. Her serum tested positively with control platelets in the MAIPA assay performed using monoclonal antibodies (MoAb) to glycoprotein (GP) IIIa (XIIF9, Y2/51), yet was negative in the presence of MoAbs to GP IIb (SZ 22) or to the GP IIb-IIIa complex (AP2, P2). The patient's platelets failed to aggregate with all agonists tested except for ristocetin. IgG isolated from the patient's serum inhibited ADP-induced aggregation of control platelets. Unexpectedly, flow cytometry showed an altered expression of membrane glycoproteins on the patient's platelets. Levels of GP Ib-IX were much higher than previously located by us in platelets. In contrast, the expression of GP IIb-IIIa was about half that seen with control subjects. When Western blotting was performed, a striking finding was a strong band of 250 kDa recognized by a series of MoAbs to GP Ib alpha in addition to the band in the normal position of GP Ib alpha. Finally, ADP-stimulated (E.B.) platelets failed to express activation-dependent epitopes on GP IIb-IIIa as recognized by PAC-1, AP6, or F26 and additionally gave a reduced P-selectin expression after thrombin addition. In conclusion, we present a novel patient with a severely perturbed platelet function where an altered membrane GP profile is associated with the presence of an autoantibody recognizing a complex-dependent determinant on GP IIb-IIIa and inhibitory of platelet aggregation.

A close spatial relationship between GP IIb-IIIa complexes and CD9 antigen as demonstrated by the MAIPA technique

CD9 is a well-defined component of the platelet plasma membrane and has a copy number almost equivalent to that of glycoprotein (GP) IIb-IIIa complexes, the aggregation receptor on platelets. It has an apparent molecular mass of 24 kD and is otherwise known as p24. Stimulation of p24 by monoclonal antibodies (MAb) induces platelet aggregation and granule release, involves FcγRII, and is mainly mediated through the stimulation of phospholipase C. In accordance with a signalling function, p24 has been reported to associate with small GTP-binding proteins and to GP IIb-IIIa complexes upon activation. We now report further evidence of a strong relationship between p24 and GP IIb-IIIa in platelets. Using the MAIPA (monoclonal antibody immobilization of platelet antigens) assay in the screening of human antibodies to platelet glycoproteins, we found that GP IIb-IIIa-antibody complexes were almost invariably associated with p24 in the harvested detergent-soluble fraction of platelet lysates. Thus, associated human antibodies were detected following the targeting of either GP IIb-IIIa or p24 by monospecific murine monoclonal antibodies (MAbs). This is a point to bear in mind when assessing for antibodies to p24 or GP IIb-IIIa in immune thrombocytopenias.