Detection of delayed hypersensitivity reaction in rats by radioisotopic footpad assay with sodium deoxycholate extract and mitomycin-C-treated tumor cells.

Immune response in WKA rats immunized with methylcholanthrene-induced KMT-17 tumor was measured by radioisotopic footpad assay. The assay was specific, quantitative, and objective compared with the ordinary method of measuring the thickness of footpads. The strongest footpad reaction was observed 24 hr after injection of the antigens. The reaction was transferred by lymphoid cells but not by serum. These results indicate that the footpad assay manifests delayed-type hypersensitivity to tumor antigens. In order to obtain more reliable antigen preparation for the footpad assay, antigens prepared by several methods were compared. Solubilized antigen extracted with sodium deoxycholate (DOC) showed the strongest reaction in the immunized host and weak reaction in the control non-immunized host. This marked difference between the immunized and control groups indicates that DOC-extracted antigen was better antigen than tumor cells treated with mitomycin-C (40 microgram/ml), formaldehyde solution (0.2%, 0.01%), X-irradiation (3,500, 10,000 rad), non-treated whole-cell antigen, crude membrane, cell homogenates, or antigens extracted by hypotonic sonication and 3M KCl method. The DOC-extracted antigen was well preserved at -20 degrees for 1 month.