Walter P. Drake

In vivo abrogation of serum C3 and C5 by administration of cobra venom factor and heterologous anti-C3

Abstract In this study, the effectiveness of cobra venom factor and heterologous anti-C3 in depleting the various components of complement in guinea pigs was compared. Although C5 was abrogated in vivo after injection of cobra venom factor alone, circulating C3 could only be completely abolished by injection of heterologous anti-C3 subsequent to cobra venom factor treatment. Because of the need to fully abrogate C3 in order to study the role of this component in various immunopathological mechanisms, data relating to the use of both cobra venom factor and anti-C3 are presented.

The enhancement of antitumor antibody binding to cross reactive normal tissue antigens. A complement-mediated effect.

SUMMARY This paper deals with the complement-mediated binding of heterologous inactivated antimouse EL4 lymphoma to cross reactive antigens present in C57BL/6 mice. Although a comparison of in vitro absorptions using either EL4 cells or spleen cells indicates that this antitumor serum binds more avidly to tumor cells, the availability of complement during the absorption enhances the avidity for cross reactive spleen cell antigens and results in more antibody being bound than that observed in the absence of complement. When anti-EL4 serum produced in the burro was injected into C57BL/6 mice bearing EL4 lymphoma, antibody activity against EL4 target cells was absorbed out of the peripheral circulation to a greater extent (20 ×) than when this antiserum was similarly injected into normal C57BL/6 mice. However, if either exogenous rabbit or guinea pig complement was injected simultaneously with this antiserum, the absorption of antibody by normal mice was increased and could be shown to mimic the absorption of antibody originally obtained without complement in the tumor-bearing animals. Inactivation of guinea pig C3 by cobra venom factor altered the ability of guinea pig complement to cause increased antibody binding in vivo. Complement-sufficient serum heated at 56 C for 35 min lost all ability to enhance in vivo antibody absorption. However, complement heated for only 10 min, while unable to lyse sensitized cells in vitro, reacted similarly to untreated complement in vivo with respect to increasing antibody binding to cross reactive antigens, further imputing a key role to exogenous C3 in this mechanism. Guinea pig complement, reconstituted from the nine functionally purified components, also resulted in increased absorption of antibody in vivo. Similar results obtained in vitro are best explained by the proposition that in the reversible reaction, Ab + Ag Ab · Ag, the availability of complement, functionally reactive with the antibody, enhances the avidity of anti-EL4 for weakly cross reactive antigens on normal cells and thus favors the formation of those complexes which, in the absence of complement, occur only to a minimal extent.