Activation of the alternative complement pathway by IgM antibody reacted on paragloboside incorporated into liposome membrane

Abstract Liposomes containing paragloboside (PC) on their membrane were readily lysed by C4 deficient guinea pig serum (C4D-GPS). On the other hand, guinea pig serum from specific pathogen free Hartley guinea pigs (SPF-GPS) did not lyse PG-liposomes in Mg-EGTA-GVB (gelatin veronal buffered saline containing MgCl 2 and ethyleneglycol-bis(β-aminoethyl ether)N,N'-tetraacetate) which permits complement activation via the alternative pathway but not via the classical pathway. However, the SPF-GPS could lyse the liposomes in Mg-EGTA-GVB when heated (56°C, 30 min) C4D-GPS or other guinea pig serum (GPS) was added. Gel filtration of Hartley (Htl)-GPS through a Sephadex G-200 column revealed that IgM antibody to PG in Htl-GPS was responsible for sensitization of the liposomes to lysis by complement of SPF-GPS via the alternative pathway. This result indicated that guinea pig IgM antibody can initiate the activation of the alternative pathway of homologous complement on liposome membrane.