In situ separation of bacterial trapping and killing functions of the perfused liver.

CF-1 mice cleared and killed 80% of a 1.2 x 10(9) intravenous dose of Salmonella typhimurium after 30 min. The perfused mouse liver trapped 70% of a similar dose of S. typhimurium in a single pass, but in the perfusion model no significant killing of the trapped organisms was observed. The perfused rat liver also avidly trapped bacteria. Because of its larger size, we have been able to devise techniques to experimentally distinguish between the bacterial trapping and killing functions of this organ. When the liver was washed free of blood with sterile M-199, over 70 to 80% of a 10(6) to 10(10) dose of viable S. typhimurium was trapped after a single pass, but no significant bacterial killing was observed. When blood or plasma was added to the perfusion medium, over 50% of the trapped bacteria were killed in 15 to 30 min. Phase contrast and electron micrographs of perfused livers showed extensive extracellular trapping of bacteria in the sinusoids. Our data show that humoral factors are apparently not necessary for efficient trapping of live Salmonella by the perfused rat liver but are an absolute requirement for bacterial activity of the organ.