Circulating IgA immune complexes in head and neck cancer, nasopharyngeal carcinoma, lung cancer, and colon cancer.

A double antibody enzyme-linked immunosorbent assay (ELISA) was developed to quantitate circulating immune complexed IgA (IgA IC) in human serum. The serum panel for this study consisted of normal blood donors, benign surgery (BS), head and neck cancer (HN), nasopharyngeal carcinoma (NPC), lung cancer (LC), and colon cancer (CC) patients. Immune complexes (IC) were isolated from these sera by precipitation with 3.5% polyethylene glycol (PEG), washed and then redissolved in 0.1 M phosphate-buffered saline pH 7.2. The amount of IgA IC present were then quantified using the double antibody IgA ELISA. This assay was found to be both sensitive (26.0 ng/ml) and reproducible (intra-assay coefficient of variation 4.0%). The mean IgA IC for each cancer group tested (HN = 11.38 +/- 12.54 micrograms/ml; NPC = 13.36 +/- 17.56 micrograms/ml; LC = 17.39 +/- 13.04 micrograms/ml; CC = 26.50 +/- 4.60 micrograms/ml) were significantly elevated (P = 0.001) over both the normals (5.12 +/- 4.09 micrograms/ml) and the benign surgery controls (5.92 +/- 5.04 micrograms/ml). In addition to providing a new tumor marker the presence of high levels of IgA IC in cancer patients could provide a source of tumor-specific antibody as well as antigen and provide reagents to study immune regulation in cancer patients.