Injection of the immuno-modulatory drug alpha-galactosylceramide results in the recruitment of a large population of antigen-presenting cells into the liver of C57BL/6 mice

Rapid activation and hepatic recruitment of innate-like regulatory B cells after invariant NKT cell stimulation in mice

BACKGROUND & AIMS

Invariant natural killer T (iNKT) cells are present within the liver and have been implicated in the development of many liver diseases. Upon activation by glycolipid ligands (including α-galactosylceramide; αGalCer), hepatic iNKT cells produce numerous cytokines and recruit both pro-inflammatory and regulatory immune cells. However, the involvement of B cells in this process is poorly defined.

METHODS

Wild-type (male, C57BL/6), B cell deficient, or B cell depleted mice were injected with αGalCer or vehicle, hepatic B cell phenotype and liver injury was subsequently determined.

RESULTS

iNKT cell activation resulted in liver injury and the rapid activation and hepatic recruitment of B cells (mainly innate-like B1 and MZ-like B cells) from the spleen and peritoneal cavity. B cells recruited to the liver produce IL-10 and TGFβ, and express cell surface CD73 (ectoenzyme which generates adenosine). B cell deficient mice developed augmented αGalCer-induced hepatitis, enhanced neutrophil recruitment and striking alterations in the hepatic cytokine milieu. αGalCer-induced hepatitis was unaltered in IL-10(-/-) mice, or after TGFβ neutralization, but was significantly worsened in mice treated with a CD73 inhibitor.

CONCLUSIONS

iNKT cell stimulation recruits innate-like regulatory B cells to the liver which suppress hepatic inflammation through IL-10 and TGFβ1 independent mechanisms, but involve CD73 activity. These findings highlight an important inflammation suppressing role for B cells at early time points during the development of an innate immune response within the liver, and represent a potential therapeutic target for the treatment of liver disease.

Protective role of interleukin-17 in murine NKT cell-driven acute experimental hepatitis

NKT cells are highly enriched within the liver. On activation NKT cells rapidly release large quantities of different cytokines which subsequently activate, recruit, or modulate cells important for the development of hepatic inflammation. Recently, it has been demonstrated that NKT cells can also produce interleukin-17 (IL-17), a proinflammatory cytokine that is also known to have diverse immunoregulatory effects. The role played by IL-17 in hepatic inflammation is unclear. Here we show that during α-galactosylceramide (αGalCer)-induced hepatitis in mice, a model of hepatitis driven by specific activation of the innate immune system via NKT cells within the liver, NK1.1+ and CD4+ iNKT cells rapidly produce IL-17 and are the main IL-17-producing cells within the liver. Administration of IL-17 neutralizing monoclonal antibodies before αGalCer injection significantly exacerbated hepatitis, in association with a significant increase in hepatic neutrophil and proinflammatory monocyte (ie, producing IL-12, tumor necrosis factor-α) recruitment, and increased hepatic mRNA and protein expression for the relevant neutrophil and monocyte chemokines CXCL5/LIX and CCL2/MCP-1, respectively. In contrast, administration of exogenous recombinant murine IL-17 before α-GalCer injection ameliorated hepatitis and inhibited the recruitment of inflammatory monocytes into the liver. Our results demonstrate that hepatic iNKT cells specifically activated with α-GalCer rapidly produce IL-17, and IL-17 produced after α-GalCer administration inhibits the development of hepatitis.

Alpha-GalCer ameliorates listeriosis by accelerating infiltration of Gr-1+ cells into the liver

Alpha-galactosylceramide (alpha-GalCer) activates invariant (i)NKT cells, which in turn stimulate immunocompetent cells. Although activation of iNKT cells appears critical for regulation of immune responses, it remains elusive whether protection against intracellular bacteria can be induced by alpha-GalCer. Here, we show that alpha-GalCer treatment ameliorates murine listeriosis, and inhibits inflammation following Listeria monocytogenes infection. Liver infiltration of Gr-1+ cells and gamma/delta T cells was accelerated by alpha-GalCer treatment. Gr-1+ cell and gamma/delta T-cell depletion exacerbated listeriosis in alpha-GalCer-treated mice, and this effect was more pronounced after depletion of Gr-1+ cells than that of gamma/delta T cells. Although GM-CSF and IL-17 were secreted by NKT cells after alpha-GalCer treatment, liver infiltration of Gr-1+ cells was not prevented by neutralizing mAb. In parallel to the numerical increase of CD11b+Gr-1+ cells in the liver following alpha-GalCer treatment, CD11b-Gr-1+ cells were numerically reduced in the bone marrow. In addition, respiratory burst in Gr-1+ cells was enhanced by alpha-GalCer treatment. Our results indicate that alpha-GalCer-induced antibacterial immunity is caused, in part, by accelerated infiltration of Gr-1+ cells and to a lesser degree of gamma/delta T cells into the liver. We also suggest that the infiltration of Gr-1+ cells is caused by an accelerated supply from the bone marrow.