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Summary. Leucocyte adhesion is an important phenomenon in antimicrobial defence, inflammation and immunological mechanisms and has been shown to be dependent upon specialized adhesion molecules. To prevent side-effects related to blood transfusion (e.g. anti-human leucocyte antigen immunization and transmission of infectious agents) leucocyte reduction of blood products is now systematically performed in various countries. The most common system used for leucoreduction is blood filtration. For further understanding of the mechanisms responsible for the interaction between leucocytes and the fibres present in filters we used a flow chamber to study the adhesion of leucocytes and leukaemic cell lines to different types of fibre. Adhesion was quantified using video-microscopy and computer image analysis. Our results demonstrate that adhesion to filter fibres was dependent on the expression of b2-integrins CD11±-CD18 and was inhibited by anti-CD18. The amount of fibres present, their spatial arrangement and the physicochemical characteristics of the fibres were important factors in leucocyte adhesion. Leucocyte adhesion was the highest to polyethylene terephthalate (PET) and polyimide fibres. Lymphocytes or lymphocytic cell lines were poorly adherent to PET fibres. The retaining capacity of leucocyte filters can be improved by taking into account the different parameters for the design of new filters

The effect of lupus anticoagulant (LA) positive plasma on the expression of human monocyte procoagulant activity (PCA) was studied. LA positive plasma were able to enhance the endotoxin or TNF alpha induced monocyte associated PCA. The monocyte PCA had the characteristic of tissue factor activity (factor VII, factor X dependence). The enhancement of monocyte PCA could be confirmed using purified LA positive IgG. The stimulating effect was supported by the F(ab')2 fragments.

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