ACTIVATION OF THE ALTERNATIVE COMPLEMENT PATHWAY OF GUINEA-PIG BY LIPOSOMES INCORPORATED WITH TRINITROPHENYLATED PHOSPHATIDYLETHANOLAMINE

  • 1 January 1982
    • journal article
    • research article
    • Vol. 45  (1) , 115-124
Abstract
By incorporation of trinitrophenylaminocaproyldipalmitoylphosphatidylethanolamine (TNP-Cap-DPPE) into liposomes composed of an equimolecular mixture of dimyristoylphosphatidylcholine (DMPC) and cholesterol (TNP-Cap-liposomes), liposomes became readily lysed by guinea pig serum (GPS) in Mg2+-EGTA-GVB (gelatin veronal buffered saline containing 2 mM MgCl2 and 10 mM ethyleneglycol-bis(.beta.-aminoethyl ether)N,N,N''N''-tetraacetate) and in GVB2+ (gelatin veronal buffered saline containing 0.15 mM CaCl2 and 0.5 mM MgCl2). Since the classical complement pathway (CCP) does not work in Mg2+-EGTA-GVB, TNP-Cap-liposome lysis by GPS in Mg2+-EGTA-GVB was thought to be mediated by the activation of the alternative complement pathway (ACP). This conclusion was supported by observations that heating of GPS at 50.degree. C impaired its lytic activity while C4-deficient GPS was capable of lytic activity, no lysis occurred in EDTA and there was consumption of complement in GPS treated with TNP-Cap-liposomes at 30.degree. C. For TNP-Cap-liposome lysis by GPS in Mg2+-EGTA-GVB, the epitope density of the TNP hapten was required to be .gtoreq. 5% of the DMPC. Changing the acyl group of the phosphatidylcholine (PC) significantly influenced the ACP activating capacity of TNP-Cap-liposomes. Dipalmitoyl-PC, DMPC and distearoyl-PC facilitated the ACP activating capacity of the TNP-Cap-liposome while dilauroyl-PC, egg-PC and dioleoyl-PC did not. The length of spacer between TNP and dipalmitoylphosphatidylethanolamine (DPPE) also influenced the ACP activating capacity and maximum activation was noted when the spacer was aminocaproyl. These physicochemical characteristics which increase the ACP activating capacity coincided with those reported to increase the immunogenicity of hapten-sensitized liposomes.