Elevation of natural killer activity and nonspecific immunity following injection of Listeria cell walls.

Mice given a single intraperitoneal injection of cell walls from Listeria monocytogenes (LCW) prior to challenge with Candida albicans or a mammary carcinoma showed significantly increased survival compared to saline injected controls. The cell walls were mitogenic for spleen cells in vitro. Levels of stimulation were lower than for Con A and PHA but comparable to those induced by LPS. Peritoneal exudative cells, but not spleen cells, harvested from mice injected with LCW showed significant elevation of natural killer (NK) cell activity as early as 1 day following injection. NK activity remained elevated for 10 days and then returned to normal levels by day 145. Macrophage phagocytic and tumorcidal activity in vitro did not appear stimulated. In overall comparison to commercial mitogens, LCW had lower levels of activity measured in vitro but equivalent or higher in vivo levels of protection.