Preliminary Investigation of the Immunomodulatory Capacity of Mixed Lactobacillus plantarum by in Vitro and in Vivo Experiments

Objective: To study the immunomodulatory capacity of Lactobacillus plantarum mixed by in vitro and in vivo experiments. Methods: The effect of Lactobacillus plantarum mixed on the proliferative capacity of macrophages was observed using the CCK8 method. The effect of Lactobacillus plantarum mixed on macrophage phagocytosis was detected using the macrophage phagocytosis neutral red method. NO, TNF-α, IL-6, IL-1β kits were used to determine the macrophage-promoting cytokine secretion capacity of Lactobacillus plantarum mixed. Healthy BALB/c mice were randomly divided into three groups: normal group (NC group), model group (MC group), and Lactobacillus plantarum mixed group (Mix group). The body weight of laboratory mice before, after and at the end of modeling was recorded, and the spleen and thymus indexes of each experimental group, as well as the proliferation ability of spleen lymphocytes and the activity of natural killer cells (NK) after the mice died were measured. Results: Lactobacillus plantarum mixed was not cytotoxic and significantly promoted macrophage proliferation at MOI=1, 10, and 100 compared to the normal group (P<0.05) (MOI=1, 10, 100, and 1000. 1, 10, 100, and 1000 represented the number of Lactobacillus plantarum mixed infected with the RAW 264.7 macrophage complex, respectively, (MOI) of 1:1, 10:1, 100:1, and 1000:1). The highest relative proliferation rate of Lactobacillus plantarum mixed was 176.75% when MOI=100. Lactobacillus plantarum mixed significantly increased phagocytosis of macrophages at all MOI values (P<0.05) and showed excellent immune activity compared to the normal group. Especially at MOI=100, the phagocytic activity of cells in the Lactobacillus plantarum mixed group (A₅₄₀=0.80) was significantly better than that in the LPS group (A₅₄₀=0.55) (P<0.05). The Lactobacillus plantarum mixed group significantly up-regulated the levels of NO and cytokines secreted by macrophages compared to the normal group when MOI=1, 10 and 100 (P<0.05). Macrophage NO secretion was 27.32 µmol/L, TNF-α secretion was 116.97 pg/mL, IL-6 secretion was 41.98 pg/mL, and IL-1β secretion was 149.88 pg/mL when MOI=100. Lactobacillus plantarum mixed intake increased body weight, up-regulated spleen index and thymus index in mice compared to MC. Lactobacillus plantarum mixed also had a significantly pro-proliferative effect on splenic lymphocyte damage caused by cyclophosphamide (P<0.05). Compared with MC group, Mix group could significantly increase the activity of NK cells in mice (P<0.05), reached 41.72%. Conclusion: Lactobacillus plantarum mixed has immunomodulatory activity and is a good immunomodulator.