Peritoneal exudate macrophage monolayers (PEMM) from C57BL/6 and DBA/2 mice inoculated ip with
tumor allografts were induced to release in vitro labile cell toxin(s), herein called "macrophage
cytotoxin(s)" (MCT). Macrophages released MCT spontaneously for a short interval when initially established as monolayers, and they were reinduced to secrete MCT by exposure to allogeneic and syngeneic
tumor cells (but not to normal cells) and by exposure to
polyinosinic-polycytidylic acid (
poly I .
poly C) and
lipopolysaccharide (LPS). PEMM from normal mice treated ip 3 days previously with thioglycollate were also induced to release toxins in vitro. These cells did not release MCT spontaneously before or
after treatment with neoplastic cells but were induced to release MCT by exposure to
poly I .
poly C or LPS. Resident peritoneal macrophages did not release MCT either spontaneously or
after treatment with
tumor cells,
poly I .
poly C, or LPS. MCT released from alloimmune mice stimulated with syngeneic or allogeneic
tumor cells were resolved by molecular sieving into a major peak at 140,000--160,000 daltons, called "alpha-MCT," and into a minor peak at 60,000 daltons, called "beta-MCT." However, supernatants from thioglycollate-induced PEMM, stimulated with
poly I .
poly C or LPS, appeared to be composed entirely of the alpha-class. alpha-MCT from
poly I .
poly C-stimulated PEMM caused 31--56% lysis of syngeneic EL-4 and allogeneic L-929,
NS-1, and YAC-1
tumor cells in vitro but was not cytotoxic for normal cells. Secretion of the MCT by PEMM derived from thioglycollate-treated animals stimulated with
poly I .
poly C was inhibited by
colchicine,
emetine,
iodoacetic acid,
trypan blue, and
cytochalasin B.