Selective effects of Lactobacillus casei Shirota on T cell activation, natural killer cell activity and cytokine production

Abstract

Modulation of host immunity is an important potential mechanism by which probiotics confer health benefits. This study was designed to investigate the effects of a probiotic strain, Lactobacillus casei Shirota (LcS), on immune function using human peripheral blood mononuclear cells (PBMC) in vitro. In addition, the role of monocytes in LcS-induced immunity was also explored. LcS promoted natural killer (NK) cell activity and preferentially induced expression of CD69 and CD25 on CD8(+) and CD56(+) subsets in the absence of any other stimulus. LcS also induced production of interleukin (IL)-1beta, IL-6, tumour necrosis factor (TNF)-alpha, IL-12 and IL-10 in the absence of lipopolysaccharide (LPS). In the presence of LPS, LcS enhanced IL-1beta production but inhibited LPS-induced IL-10 and IL-6 production, and had no further effect on TNF-alpha and IL-12 production. Monocyte depletion reduced significantly the impact of LcS on lymphocyte activation, cytokine production and natural killer (NK) cell activity. In conclusion, LcS activated cytotoxic lymphocytes preferentially in both the innate and specific immune systems, which suggests that LcS could potentiate the destruction of infected cells in the body. LcS also induced both proinflammatory and anti-inflammatory cytokine production in the absence of LPS, but in some cases inhibited LPS-induced cytokine production. Monocytes play an important role in LcS-induced immunological responses.

Fig. 1

Effect of Lactobacillus casei Shirota (LcS) on expression of CD69 and CD25 by lymphocytes. Peripheral blood mononuclear cells (PBMCs) were cultured with live L. casei Shirota at 10⁵, 10⁶ or 10⁷ colony-forming units (CFU)/ml in the presence or absence of concanavalin A (ConA) (2·5 µg/ml). Non-stimulated cultures were shown as negative control. Each bar represents the mean of 6 to 19 blood donors and the error bars represent standard deviation [49]. *P < 0·05, **P < 0·01, ***P < 0·001 compared with non-stimulated cultures.

Fig. 2

Effect of Lactobacillus casei Shirota (LcS) on production of cytokines by peripheral blood mononuclear cells (PBMCs) in the presence or absence of lipopolysaccharide (LPS). PBMCs were cultured with live LcS at 10⁶ colony-forming units (CFU)/ml for 24 h in the presence or absence LPS (1 µg/ml). Non-stimulated cultures were shown as negative control. Each bar represents the mean of 6 to 12 blood donors and the error bars represent standard deviation [49]. *P < 0·05, **P < 0·01,***P < 0·001 compared with non-stimulated cultures.

Fig. 3

Effect of monocyte depletion on Lactobacillus casei Shirota (LcS)-induced CD69 and CD25 expression by peripheral blood mononuclear cells (PBMCs) and monocyte-depleted (MD)-PBMCs. (a) CD69 expression; (b) CD25 expression. PBMCs or MD-PBMCs were incubated with medium or live LcS at 10⁶ colony-forming units (CFU)/ml for 24 h. Data are shown as mean ± standard deviation of 6 to 19 subjects. *P < 0·05, **P < 0·01, ***P < 0·001 compared between PBMC and MD-PBMC cultures.

Fig. 4

Effect of monocyte depletion on Lactobacillus casei Shirota (LcS)- and lipopolysaccharide (LPS)-induced cytokine production. Peripheral blood mononuclear cells (PBMCs) or monocyte-depleted (MD)-PBMCs were incubated with live LcS at 10⁶ colony-forming units (CFU)/ml or LPS at 1 µg/ml for 24 h. Increase of cytokine productions of interleukin (IL)-1β, IL-6, tumour necrosis factor (TNF)-α, IL-12 and IL-10 in the supernatants of the cultures were measured by enzyme-linked immunosorbent assay. Data are shown as mean ± standard deviation of 6 to 14 subjects. *P < 0·05, **P < 0·01, ***P < 0·001 compared between PBMC and MD-PBMC cultures.

Fig. 5

Effect of Lactobacillus casei Shirota (LcS) on natural killer (NK) cell activity in peripheral blood mononuclear cells (PBMCs) and monocyte-depleted (MD)-PBMCs. PBMCs or MD-PBMCs were incubated with medium or live LcS at 10⁶ colony-forming units (CFU)/ml for 24 h. NK cell activity represented by percentage of specific lysis of target cells was assessed in freshly prepared PBMCs (a), in PBMCs cultured with medium or LcS (b) and in MD-PBMCs cultured with medium or LcS (c) for 24 h. Data are shown as mean ± standard deviation of five subjects. *P < 0·05, **P < 0·01, ***P < 0·001 compared with non-stimulated cultures of PBMC or MD-PBMC.