A Radioisotopic Microassay for Lymphotoxin Using Technetium-99 Labeled Cells 1 2

Summary

We have developed a new micro-assay for lymphotoxin utilizing murine l-929 target cells prelabeled with technetium-99m, a high specific activity, metastable gamma emitter which is bound to living cells and not released in appreciable quantities by dead or injured cells. Target l-cells prelabeled with ^99mTc were added to micro tissue culture plates at a concentration of 10,000 cells/well. Eighteen hr later lymphotoxin or control material was added and the cells were incubated for an additional 12–28 hr. A maximum cytocidal effect was observed after incubation of target cells for 28 hr with 100 CU of lymphotoxin. The number of surviving adherent cells as determined by gamma counting for ^99mTc was in accord with that recorded by visual enumeration. The ^99mTc microassay is a sensitive, easily performed, rapid test for lymphotoxin activity which appears to have a number of advantages over previously reported in vitro methods.

We thank Mrs. L. Williams and S. Vaishnav for technical assistance and Mrs. K. Phipps and E. Olson for secretarial help.