Immunopotentiating activity of whole cells and mini-cells of Salmonella typhimurium

Salmonella typhimurium strain 9 produces mini-cells during cell proliferation. Mini-cells are viable but cannot proliferate since they do not contain chromosomal DNA. Effects of whole cells and mini-cells of S. typhimurium on the immune responses were investigated, with the following results. Phagocytosis of peritoneal macrophages was enhanced by in vivo stimulation of both whole cells and mini-cells. Cellular immunity against L1210 cells (mouse leukemia cells) and Sarcoma 180 cells was also enhanced by both whole cells and mini-cells. Mini-cells slightly stimulated in vitro blast cell transformation of normal mouse lymphocytes. Whole cells of S. typhimurium induced antibody-forming cells to produce IgG of higher affinity but mini-cells did not. Mini-cells were not directly cytotoxic for normal lymphocytes or L1210 cells.