Essential role of Toll-like receptors for dendritic cell and NK1.1⁺ cell-dependent activation of type 1 immunity by Lactobacillus pentosus strain S-PT84

Activation of type 1 immunity plays a critical role in host defense mechanisms against infectious disease and tumor. Lactic acid bacteria, existing in the gastrointestinal tract, are one of the powerful tools to induce a type-1-dominant immunity, which may improve Th2-dependent allergic diseases. In the present work, we found that an oral intake of Lactobacillus pentosus strain, S-PT84 into mice significantly enhanced NK activity of spleen cells in vivo. We further revealed that NK1.1 positive NK cells and NKT cells are responsible cells for producing IFN-γ after stimulation with S-PT84 in vitro. S-PT84 induced IFN-γ-producing cells through activation of IL-12 production by CD11c⁺DCs in Toll-like receptor (TLR) 2- and/or TLR4-dependent manner. Interestingly, direct interaction between DCs and NK1.1⁺ cells was also essential for the IFN-γ production in response to the S-PT84 stimulation. Therefore, we concluded that S-PT84 effectively promoted type 1 immunity through IL-12 and IFN-γ which were produced by DCs and NK1.1⁺ cells, respectively. Thus, S-PT84 would be a nice immune modulator for improving immunobalance, which plays a pivotal role for controlling allergy, infectious diseases and tumor.