Characterization of serum protein components from Donryu rats which were immune to hepatoma AH-66 tumor cells

Immune serum from Donryu rats which resisted rechallenge with 5 X 10(6) AH-66 tumor cells (1000 X Threshold) was examined for reactivity with these cells using three assays: 1) tumor cell agglutination 2) immunofluorescence and 3) complement mediated cytotoxicity. Whole immune serum and its components had different levels of activities in the various assays and differences in their antigenic specificities were also observed. Whole immune serum showed some activity in all assays to AH-66 tumor cells. Its specificity and that of the IgG "enriched" fraction (insoluble in 40% sat. AmSO4) was studied using the agglutination assay. A general cross-reactivity was seen with all tumor cell lines. These reactions could be eliminated by absorption of the serum or serum fraction with tumor lines other than AH-66 or with embryonic tissue. An IgG "free" derived from the 40% sat. AmSO4 precipitate showed only agglutinin activity but this reactivity, even to AH-66 tumor cells, was abrogated by absorption with embryonic tissue. Incubation of the IgG "free" fraction with tumor target cells blocked the complement mediated cytotoxicity and the immunofluorescence reactivities of the whole immune serum. The alpha 2 macroglobulin component of the IgG "free" fraction appeared to be responsible for its agglutinin activity.