Toxicity of Na251CrO4 when used to label rat lymphocytes

Lymphocytes preincubated with various activities of Na251CrO4 were tested for their ability to induce a local, popliteal lymph node graft-versus-host (GVH) reaction. Incubation with 100 micronCi of the isotope per ml of cell suspension impaired the GVH activity, 25 micronCi gave a reduced response in 1 out of 3 experiments, whereas 10 micronCi had no effect. The reduced GVH response was due to radiation rather than chemical damage of the cells. Preincubation of the cells with either cold Na2CrO4 or outdated Na251CrO4 with concentrations of Cr identical to the ones used to label cells with 100 micronCi/ml cells did not impair the GVH reactivity. The cellular uptake of Na251CrO4 showed first-order kinetics over wide concentration ranges. Mitomycin C-treated lymphocytes showed a more heavily depressed GVH reactivity than would be expected from their moderately reduced ability to accumulate in the lymph nodes. It is recommended that doses of Na251CrO4 in excess of 10 micronCi/ml cells should not be used for functional studies of lymphocytes.