Enhancement of hematopoietic response of mice by subcutaneous administration of Lactobacillus casei.

Mice that had received heat-killed Lactobacillus casei (LC 9018) subcutaneously (s.c.) showed enhanced resistance to systemic (i.e., intravenous) infection with Listeria monocytogenes, but the antilisterial resistance of mice was less augmented by s.c. administration of Propionibacterium acnes ("Corynebacterium parvum"). Though there was little change in the total number of splenic leukocytes after s.c. administration of LC 9018, the monocyte-macrophage ratio increased after treatment, reaching its peak on day 5 to 7 after injection. The number of progenitor cells that form macrophage colonies under the stimulus of L-cell-conditioned medium in a semisolid agar culture system increased in the spleens of mice pretreated s.c. with LC 9018, showing a peak response on day 5 after injection. The increase corresponded to the increase in the dose administered, and increased numbers were detected even 10 days after treatment. The number of macrophage colonies in the femurs of mice pretreated s.c. with LC 9018 showed a temporary increase on day 3 after injection but then a decrease until day 10. Colony-stimulating activity was detected in the sera of mice administered LC 9018 s.c. 18 h previously, and the colonies produced were of three types: granulocyte (8%), macrophage (56%), and granulocyte-macrophage (36%). Administration of C. parvum s.c. had little effect on these hematopoietic responses of mice.