Peritoneal macrophages from Sarcoma 1 (SAl)-sensitized CS7B1/6 mice release a toxic factor (s), termed macrophage toxic factor (MTF), into the medium when exposed to allogeneic target L cells in vitro. Medium containing MTF is cytotoxic to cultures of allogeneic L cells, syngeneic C57B1/6 fetal fibroblasts and xenogenic HeLa cells. The cell toxin (s) is insensitive to the effects of nuclease, neuraminidase and trypsin, but is partially abrogated by treatment with pronase. Two fractions of toxic activity are eluted from Sephadex G-100, one associated with a 150,000 mol wt marker (IgG), and the other associated with a 47,000 mol wt marker (ovalbumin). Goat antiserum prepared against PHA-induced mouse lymphotoxin (MLT) is capable of neutralizing the toxicity of both MTF and MLT, indicating that the factors may be similar. © 1972.

An In Vitro Microassay for Lymphotoxin (LT) is described. Target cell monolayers are established in the wells of a microtiter assay plate at a density of 100-500/well. Dilutions of Lymphotoxin containing medium are placed upon the target cell monolayers. The plates are sealed with a gas impervious film, and the cells are incubated for 24-48 hr. The cell numbers in each well are established initially, and after the incubation period. The percent destruction is based upon total cell counts of experimental wells compared to control wells. Comparison of the assay to the previously described assay, which is based upon ability of cells to incorporate 14C amino acids into protein, with several batches of LT, shows the microassay to be 25 × more sensitive than the latter. Other advantages and disadvantages of the assay system are also described. © 1972.