Renaud Lavend'homme

Human liver sinusoidal endothelial cells but not hepatocytes contain factor VIII.

Although the liver is the major site of coagulation factor VIII (FVIII) synthesis, the type of cells producing FVIII within the liver is still unclear.

Activation of human endothelial cells from specific vascular beds induces the release of a FVIII storage pool

Although the liver is known to be the main site of factor VIII (FVIII) production, other organs are probably also important for the regulation of FVIII secretion. However, the study of the regulation of extrahepatic FVIII production has been hampered by the lack of definitive identification of human tissues able to secrete FVIII. Recent studies have shown that lung endothelial cells can synthesize FVIII. We therefore studied the production of FVIII by endothelial cells purified from other vascular beds. Because physiologic stress results in a rapid elevation of FVIII, we also investigated whether endothelial cells can store FVIII and secrete it after treatment with agonists. Microvascular endothelial cells from lung, heart, intestine, and skin as well as endothelial cells from pulmonary artery constitutively secreted FVIII and released it after treatment with phorbol-myristate acetate and epinephrine. By contrast, endothelial cells from the aorta, umbilical artery and umbilical vein did not constitutively secrete FVIII or release it after treatment with agonists, probably because of a lack of FVIII synthesis. Extrahepatic endothelial cells from certain vascular beds therefore appear to be an important FVIII production and storage site with the potential to regulate FVIII secretion in chronic and acute conditions.

Variable region heavy chain glycosylation determines the anticoagulant activity of a factor VIII antibody.

Summary.  Background: N‐glycosylation occurs in the variable region of about 10% of antibodies but the role of carbohydrate at this location is still poorly understood. Objectives: We investigated the function of N‐glycosylation in the variable region of the heavy chain of a human monoclonal antibody, mAb‐LE2E9, that partially inhibits factor VIII (FVIII) activity during coagulation. Methods and results: Enzymatic deglycosylation indicated that the oligosaccharides do not determine the affinity of the antibody but enhance its FVIII neutralizing activity. A mutant antibody lacking the N‐glycosylation site in the variable region of the heavy chain inhibited FVIII activity by up to 40%, while inhibition by the native antibody was 80%. To evaluate the physiological effect of such a FVIII inhibition, we investigated the ability of the mutant antibody devoid of N‐glycosylation in the variable region to prevent thrombosis in mice with a strong prothombotic phenotype resulting from a type II deficiency mutation in the heparin binding site of antithrombin. Despite its moderate inhibition of FVIII activity, the mutant antibody significantly prevented thrombosis in treated animals. We also carried out glycan analysis of native and mutant antibodies. Conclusions: Modification of glycosylation in the variable region of antibodies contributes to the diversity of FVIII type II inhibition possibly by steric hindrance of the active site of FVIII by glycans, and may provide a novel strategy to modulate the functional activity of therapeutic antibodies.

Antielastin B-cell and T-cell immunity in patients with chronic obstructive pulmonary disease

Rationale Antielastin autoimmunity has been hypothesised to drive disease progression in chronic obstructive pulmonary disease (COPD). The proposed mechanism is currently disputed by conflicting data. The authors aimed to explore antibody responses against elastin in a large and extensively characterised COPD population and to assess elastin-specific peripheral T-cell reactivity in a representative subgroup. Methods Antielastin antibodies were analysed with indirect ELISA on the plasma of 320 patients with COPD (Global Initiative for Chronic Obstructive Lung Disease 1–4) and 143 smoking controls. In a second group of 40 patients with COPD and smoking controls, T-cell responses against extracellular matrix (elastin, collagen I and collagen V) were determined with enzyme-linked immunosorbent spot (EliSpot) (interferon γ (IFNγ) and interleukin-2) on peripheral blood mononuclear cells and compared with the responses of 11 never-smoking controls. Results Antielastin antibody titres were not elevated in patients with COPD compared with smoking controls and even decreased significantly with increasing severity of COPD (p<0.001). Lower antielastin antibody titres were also found in a subgroup of patients with CT-proven emphysema. Elastin-specific INFγ-mediated T helper 1 responses could not be revealed in smoking subjects with and without COPD. Collagen I-mediated T-cell responses were also absent, which contrasted with a significant increased anticollagen V response in the smoking controls and patients with COPD compared with the never smokers (p=0.008). Collagen V-mediated T-cell responses could not discriminate between patients with COPD and smoking controls. Conclusion A systemic immune response against elastin could not be identified in patients with COPD. By contrast, collagen V-mediated autoimmunity was increased in the subgroup of smokers and may potentially contribute to the pathogenesis of COPD.

The amplitude of coagulation curves from thrombin time tests allows dysfibrinogenemia caused by the common mutation FGG-Arg301 to be distinguished from hypofibrinogenemia

Thrombin time (TT) tests are useful for diagnosing coagulation disorders involving abnormal fibrinogen but do not allow us to distinguish between qualitative and quantitative defects. However, with the widening availability of optical coagulation automates, more information about the coagulation process is becoming increasingly accessible.