Immune complexes with antiglobulin activity in sera of Moloney sarcoma-bearing rats

Immune complexes (IC) were detected and isolated from the serum of Brown Norway (BN), (Lewis x BN)F1, and Lewis rats bearing a Moloney sarcoma (MST). IC were isolated from the serum of individual rats employing a system of G-200 chromatography and passage through a heavy chain specific anti-rat IgG Immunoadsorbent. IgG and IgM were identified in the isolated IC by polyacrylamide gel electrophoresis (PAGE) and co-precipitation radioimmunoassays. Employing monospecific antibodies, IC consisting of IgG and IgM were bound to Raji cells as assessed by radioimmunoassay and indirect immunofluorescence. Raji binding activity of IC-containing serum was substantially reduced by pretreatment with dithiothreitol or incubation with anti-rat IgM or pooled normal rat IgG: F(ab')2. Sucrose density gradient ultracentrifugation under acid conditions dissociated IC into 7S IgG and 19S IgM components which recombined when co-incubated at pH 7 . 5. Viral antigens (gp70 and p30) were not detected in IC by PAGE and co-precipitation radioimmunoassay. Findings show that sera of rats bearing MST contain IC consisting predominantly of immunoglobulin. An IgM component which was separated, isolated and identified within IC containing serum displays anti-F(ab')2 reactivity.