Direct comparison of three isotopic release microtoxicity assays as measures of cell-mediated immunity to Gross virus-induced lymphomas in rats.

Three isotopic release microtoxicity assays--[125I]5-iodo-2'-deoxyuridine release assay (IRA), 51Cr release assay (CRA), and [3H]proline release assay (PRA)--have been utilized to measure cell-mediated immunity to (C58NT)D, a Gross virus-induced lymphoma in rats. These studies were designed so that all three assays were done under physical conditions as comparable as possible between the assays. A considerable difference was noted in the ability of one or another target cell to function well in each assay. The tissue culture line of (C58NT)D proved an excellent target cell in the long-term assays, whereas the ascites line was inadequate in these same long-term assays. The monolayer Gross virus-induced tumor cell line ERTh/G was resistant to lysis in the short-term CRA but functioned well in the long-term assays. The autologous and thymus cell controls utilized in these studies were reasonably neutral baseline controls for the evaluation of both normal and immune activity. Although all three assays were capable of measuring both natural and immune activity in this systemthe PRA appeared more sensitive at 24 hours and the IRA at 48 hours, whereas the CRA activity with these target cells was only useful in the short-term assays.