Activation of human complement by liposomes: serum factor requirement for alternative pathway activation
Mold, C.; Gewurz, H.
Journal of Immunology 125(2): 696-700
1980
ISSN/ISBN: 0022-1767 PMID: 7391575 Document Number: 164556
Liposomes were shown to activate human C or rabbit erythrocytes. Although a liposome-adsorbable serum factor was required for C3 conversion by liposomes, it was not sufficient for activation. Liposomes lacking glycolipid or CHOL could adsorb the serum factor, but did not activate the alternative pathway. The serum factor would also be adsorbed by phosphocholine-Sepharose beads. The binding site for the serum factor on the liposomes probably was the phospholipid DMPC. Studies testing the inhibition of serum factor binding by substances with structural similarity to phosphatidylcholine supported the hypothesis that binding was inhibited by phosphocholine and glycerophosphocholine. Although the role of the serum factor in activation is not known, liposomes containing dimyristoyl phosphatidylethanolamine in place of DMPC no longer require adsorbable serum factors to activate the alternative pathway. An important role for the membrane phospholipid in the activation of the alternative pathway by liposomes is indicated.