MONOCYTIN, A PROTECTING SUBSTANCE PRODUCED BY MURINE MONOCYTES.

Summary Several bactericidal substances were isolated from the supernatant of murine monocytes incubated for 2 hours at 37°C in Eagle's medium in vitro with addition of 5. typhi (Ty2). Smaller quantities of the same substances were liberated from monocytes incubated without addition of bacteria. An in vivo protecting substance has also been isolated. This substance protected mice if injected at least 4 hours before the bacterial inoculum, and the protection lasted for about 10 days, but when administered simultaneously with bacteria or after onset of infection no protection could be achieved. The substance turned out to be a basic protein, labile to acid treatment and trypsin and stable to heating at 100°C for one hour.