Immunodetection of thyroid tumors: role of immuno aggregates.

To understand the inconsistent immunodetection of tumors in vivo, a labelled monoclonal antibody (MAb) against a human follicular cancer cell line (UCLA RO 82 W-1) was used as a model for in vitro and in vivo studies. The 131I labelled MAb x RO 82 W-1 bound to its target cells (10% to 70%) mainly because of the generation of immunoglobulin aggregates. Aggregates generated by the freezing process were shown by polyacrylamide gel electrophoresis (PAGE) and their removal by filtration. When the aggregated 131I MAb x RO 82 W-1 was injected into BALB/c mice bearing UCLA RO 82 W-1 tumors, a high tumor/blood ratio was found in the large tumors. The tracer concentrated in the macroscopically visible necrotic part of the tumor was largely responsible for the scintigraphic detection. Irrelevant 131I-IgG also concentrated in necrotic regions of tumors. Scintigraphic detection of thyroid tumors in this model was related to the degree to which labeled aggregates of IgG, regardless of their specificity, localized in necrotic regions of the tumors.