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We have studied the endocytosis of tritium-labelled and of non-radioactive agarose in mouse macrophages in vitro. The endocytosis was greatest and most rapid in syngeneic mouse serum and in human serum, reaching a plateau after 12 h of incubation. Ten per cent serum was the minimum concentration giving optimal ingestion. The endocytosis appeared to be regulated by mechanisms involving complement factors C3 and B. Different pretreatments of sera, inactivating or depleting C3 and B, resulted in 70-80% reduction of endocytosis. Preincubation of agarose in untreated serum increased the endocytosis of agarose in heat-inactivated serum three-fold indicating that the essential factors were bound to agarose. Antibodies against C3 and B reduced endocytosis moderately but significantly.

When creating a non-thrombogenic surface by immobilisation of heparin, most of the biological activity of heparin as it is expressed in blood should be retained after the coupling procedure. Consequently the chemical methods used in the immobilisation procedure shall be selected so that they do not, infavorably, affect the anti-thrombin (AT) binding site, the charge distribution and charge density of heparin.To ascertain that the AT-binding sequence is not involved in the coupling procedure, we have developed a method in which heparin is coupled by end point attachment (EPA). Heparin is partially degraded with nitrous acid and fragments with reactive aldehydo functions in the reducing terminal residues are formed. These are coupled to aminated surfaces by reductive amination. The primary amines have been introduced on the substrates in different ways, depending on their hydrophobic or hydrophilic characteristics.It has been possible to furnish such complex devices as hollow fibre oxygenators, tubing sets and cannulas with the heparin surface. Heparinized oxygenators have successfully been used in vivo and clinically without and/or with limited systemic heparinization.

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