Analysis of sera from ovarian cancer patients for immune complexes

In contrast to other malignancies, circulating immune complexes (CICS) are usually not detected by conventional assays in the sera of ovarian cancer patients. However, a polyethylene glycol (PEG) precipitation assay has been reported to detect putative CICS in ovarian cancer. To determine if CICS were indeed present, we analyzed sera from 12 women with ovarian cancer. All were negative for CICS by the Raji cell assay; 5 (42%) were positive by the PEG assay. However, the PEG precipitate did not possess characteristics of immune complexes. IgG in sera or in the precipitate sedimented in sucrose gradients solely at the same rate as 7S monomeric IgG. In addition, the precipitates were not able to activate the complement system and the four IgG subclasses were present in the same relative concentration as that found in normal serum. The results suggest that it is probably a misnomer to label the material detected in ovarian cancer sera by the PEG precipitation assay as CICS. Instead a non-immune interaction of IgG with other components, possibly membrane fragments, is probably being measured.