Characterization of antigenic components of immune complexes isolated from a melanoma patient.

Immune complexes (IC) from the serum of a melanoma patient were partially purified with DEAE Affigel Blue. The IC were radioiodinated and then immobilized with activated Sepharose 4B. Immunologically bound components in the IC were dissociated with 3M MgCl2 followed by gel filtration chromatography. A distinct antigen component of about 700,000 daltons was obtained by refractionation of a region of the chromatogram containing antigenic activity by Sephacryl S-300 column chromatography. Though the antigenic component behaved as a single entity in the gel filtration, it consisted of at least five polypeptide chains that were revealed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions. However, 92,000 and 41,000 dalton subunits were predominant. This procedure may be useful for isolating tumor antigens from circulating IC of cancer patients.