Inducible Macrophage Cytotoxins. I. Biokinetics of Activation and Release In Vitro2

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Abstract
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 “α-MCT,” and into a minor peak at 60,000 daltons, called “β-MCT.” However, supernatants from thioglycollate-induced PEMM, stimulated with poly l. poly C or LPS, appeared to be composed entirely of the a-class. a-MCT from poly I · poly C-stimulated PEMM caused 31–56% lysis of syngeneic EL4 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.