Abstract
In order to reveal quantitatively interaction of complement (C) system with liposomes, we determined C3 fragments associated with the liposomes having different sizes after incubation in human plasma. The amount of C3 fragments per unit surface area on the unstable liposomes (Man-liposomes) which modified with synthesized glycolipid (cetylmannoside, Man) increased with the increase in the liposome size, whereas that of C3 fragments on the stable ones (PC-liposomes) was little found. In addition, the instability of Man-liposomes also increased with the increase in the liposome size and there was linear correlation. On the other hand, the amount of bound plasma proteins per unit surface area of liposomes was approximately constant regardless of differences of lipid composition and size, and showed no correlation with instability of the liposomes in the plasma. These in vitro results indicate that the instability of Man-liposomes is governed by the affinity of C system and the C system can recognize not only liposome surface characteristics but also liposome sizes. To demonstrate clearly the reason for the linear correlation between the affinity of C system and liposome size, we discussed the underlying mechanism based on the previous finding that the activation of C system by Man-MLVs was enhanced through classical C pathway and presented the hypothesized osculating model on the assumption that extent of C activation is governed by attachment of a C activator.
