The anti-inflammatory role of granulocyte colony-stimulating factor in macrophage-dendritic cell crosstalk after Lactobacillus rhamnosus GR-1 exposure

M Phi s are important sensory cells of the innate immune system and regulate immune responses through releasing different combinations of cytokines. In this study, we examined whether cytokines released by M Phi s in response to the probiotic bacterial strain GR-1 modulate the responses of DCs. The cytokine profile released by GR-1-treated M Phi s was characterized by low levels of TNF-alpha, GM-CSF, IL-6, and IL-12 but very high levels of G-CSF. GR-1 CM did not induce expression of the shared p40 subunit of IL-12 and IL-23 and costimulatory molecules CD80 or CD86 or increase T cell stimulatory capacity in DCs. However, in G-CSFR-deficient DCs or after antibody-mediated neutralization of G-CSF, GR-1 CM induced IL-12/23 p40 production significantly, indicating that G-CSF within the GR-1 CM inhibits IL-12/23 p40 production induced by other CM components. GR-1 CM and rG-CSF also inhibited LPS-induced IL-12 production at the mRNA and protein levels. The inhibition of IL-12 production by G-CSF was at least in part mediated through inhibition of JNK activation. Finally, splenic DCs of GR-1-injected mice produced less IL-12/23 p40 than those of PBS-injected mice in response to LPS ex vivo, and this was at least partially dependent on exposure to GR-1-induced G-CSF in vivo. Altogether, these results suggest that G-CSF modulates the IL-12/23 p40 response of DCs in the context of the probiotic GR-1 through M Phi-DC crosstalk. J. Leukoc. Biol. 89: 907-915; 2011.