A human monoclonal antibody obtained from EBV-transformed B cells with specificity for myosin

Redistribution of glycoprotein Ib within platelets in response to protease-activated receptors 1 and 4: roles of cytoskeleton and calcium

Thrombin activates human platelets by hydrolyzing the protease-activated receptors PAR-1 and PAR-4, exposing new N-terminal sequences which act as tethered ligands, and binding to glycoprotein (GP) Ib, whose surface accessibility transiently decreases when platelets are stimulated by the enzyme. In an attempt to better understand this latter process, we used the peptides SFLLRNPNDKYEPF (PAR-1-AP or TRAP) and AYPGKF (PAR-4-AP) to study whether hydrolysis of both PAR receptors leads to GPIb redistribution. Both peptides induced surface clearance of GPIb with a maximum at 2 min and 5 min for PAR-1-AP and PAR-4-AP, respectively, followed by a slow return to the surface with levels normalizing between 30 and 60 min. Translocation was associated with the formation of clusters of GPIb as revealed by fluorescence microscopy. This transient redistribution of GPIb was blocked by cytochalasin D and in large part by the membrane permeable Ca2+ chelator, BAPTA. The inhibitor of phosphatidylinositol 3-kinase and myosin light chain kinase, wortmannin, did not significantly modify internalization of GPIb, although its return to the surface was delayed for PAR-1-AP. PAR receptor-mediated association of GPIb to the insoluble cytoskeleton was blocked by cytochalasin D, while BAPTA alone increased and stabilized the presence of GPIb. Globally, immunoprecipitation experiments and analysis of the cytoskeleton confirmed that GPIb translocation is powered by a contractile mechanism involving Ca2+ mobilization, actin polymerization, and myosin incorporation into the cytoskeleton and that both PAR-1 and PAR-4 can activate this process.

Three-step purification of bacterially expressed human single-chain Fv antibodies for clinical applications

We have obtained a cell line which secretes a human monoclonal IgM (B7) reacting with the myosin heavy chain of human heart. We have constructed single-chain fragments (scFv) of B7. The scFv may be useful for the imaging of myocardial necrosis after myocarditis, cardiac drug toxicosis or graft rejection. The aim of our work was to purify the scFv for immunoscintigraphy. We describe several purification steps including immobilized metal affinity chromatography (IMAC), anti-c-myc monoclonal antibody affinity chromatography, size-exclusion chromatography with Superdex 75 HR 10/30 and ion-exchange chromatography (mini Q TM 30Q).

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.

Characterization and application of new macroporous membrane ion exchangers

A new ready-to-use unit for high-performance membrane chromatography has been characterized. Its dynamic capacity, resolving power and protein recovery were measured at different flow-rates. The binding capacity was 0.5-2 mg/cm2 with a 95% recovery at 10 ml/min irrespective of the protein concentration up to 10 mg/ml. For very-high flow-rates (50 and 100 ml/min) the recovery was 90% and 70%. At these flow-rates, the maximum back-pressure was about 0.1 MPa and was independent of the filtration area. By increasing the filtration area, a proportional capacity increase was obtained, indicating an easy scale-up. High flow-rates had only a slight effect on resolution. This new adsorber was able to purify IgM from supernatant of cell culture of a human hybridoma in less than 8 min with a high degree of purity (95%).