Glucocerebroside treatment ameliorates ConA hepatitis by inhibition of NKT lymphocytes

Administration of beta-glycolipids overcomes an unfavorable nutritional dependent host milieu: a role for a soy-free diet and natural ligands in intrahepatic CD8+ lymphocyte trapping and NKT cell redistribution

Soy-based diets are a major source of sphingolipids and play a complicated role in various aspects of the immune system. Administration of beta-glycolipids, including beta-glucosylceramide (GC), beta-lactosylceramide (LC) and a 1:1 combination of GC and LC (IGL) were shown to exert immune-modulatory effects.

AIM

To examine the effects of a soy-free diet, and several beta-glycolipids on concanavalin A (ConA)-induced hepatitis in the presence of an altered host glycolipid milieu.

METHODS

ConA hepatitis was induced in C57BL/6 mice that were fed a soy-free diet (glycolipid content 200 micromol/kg). Two hours prior to administration of ConA, animals were injected IP with GC, LC, IGL or PBS. Animals were sacrificed 6 h after ConA administration.

RESULTS

Both a soy-free diet and administration of beta-glycolipids were associated with significant alterations in the distribution of NKT cells. Specifically, there was a decrease in intrahepatic and an increase in intrasplenic NKT lymphocytes. beta-glycolipids prevented the ConA-induced intrahepatic CD8 lymphocyte trapping, not seen in mice with only a soy-free diet. Both a soy-free diet and beta-glycolipids alleviated ConA-induced hepatitis by inhibiting IL10 secretion and increasing IL12 serum levels. The effect of IGL was clinically and immunological superior to that of either glycolipid alone.

CONCLUSIONS

Both a soy-free diet and beta-glycolipids can overcome the unfavorable host milieu in the setting of ConA hepatitis. The host glycolipid milieu profoundly influenced the immune and clinical effects of various insults, and suggests that alteration of the glycolipid background of the host can serve as a novel therapeutic tool.

NKT lymphocyte polarization determined by microenvironment signaling: a role for CD8+ lymphocytes and beta-glycosphingolipids

Natural killer T-cell (NKT) regulatory lymphocytes have been shown to behave differently in various immune settings. The aim of the present study was to determine the effect of microenvironmental signaling on NKT polarization and the process of active CD8 and NKT intrahepatic lymphocyte sequestration. In an in vitro assay, double negative (DN) NKT hybridoma cells were incubated with Hep3B hepatoma cells. This caused a significant increase in the secretion of alpha-fetoprotein (AFP) from Hep3B cells. When NKT cells were exposed to beta-glucoslyceramide (beta-GC) prior to incubation, Hep3B cells exhibited increased proliferation, increased IFN secretion, and reduced AFP secretion. In vivo, the adoptive transfer of naïve DN NKT cells into athymic nude-nu mice transplanted with human Hep3B hepatocellular carcinoma (HCC) caused accelerated tumor growth. This effect was inhibited by prior ex vivo exposure of DN NKT lymphocytes to beta-GC. To assess the effect of the immunological environment on NKT cells, immune mediated hepatitis and colitis were induced simultaneously in mice. Induction of TNBS colitis prior to administration of concanavalin A (Con A) hepatitis resulted in an aggravation of the liver damage caused by Con A hepatitis alone. This effect was associated with reduced intrahepatic CD8+ T cell trapping and an increase in intrahepatic NKT cells. The presence of different ligands altered host microenvironment signaling and influenced the fate and polarization of NKT cells and the sequestration of active intrahepatic lymphocytes. These data support the notion that NKT regulatory lymphocytes have an inherent plasticity that may be important for their regulatory function.

beta-Glycosphingolipids as immune modulators

beta-Glycosphingolipids have emerged as a family of potential ligands for natural killer T (NKT)-regulatory lymphocytes. This subset of regulatory lymphocytes has been implicated in the regulation of autoimmune processes. The major histocompatibility complex (MHC) Class I-like CD1d glycoprotein is a member of the CD1 family of antigen-presenting molecules and is responsible for selection of NKT cells. beta-Glycolipids have been shown to alter immune responses in the opposing settings of autoimmune diseases or cancer. In this review, we discuss the potential use of beta-glycoshpingolipids for NKT-based immunotherapy.

Potential role of NKT regulatory cell ligands for the treatment of immune mediated colitis

Natural killer T lymphocytes (NKT) have been implicated in the regulation of autoimmune processes in both mice and humans. In response to stimuli, this subset of cells rapidly produces large amounts of cytokines thereby provoking immune responses, including protection against autoimmune diseases. NKT cells are present in all lymphoid compartments, but are most abundant in the liver and bone marrow. They are activated by interaction of their T-cell receptor with glycolipids presented by CD1d, a nonpolymorphic, major histocompatibility complex class I-like molecule expressed by antigen presenting cells. Several possible ligands for NKT cells have recently been suggested. β-glucosylceramide, a naturally occurring glycolipid, is a metabolic intermediate in the anabolic and catabolic pathways of complex glycosphingolipids. Like other β-glycolipids, β-glucosylceramide has an immunomodulatory effect in several immune mediated disorders, including immune mediated colitis. Due to the broad impact that NKT cells have on the immune system, there is intense interest in understanding how NKT cells are stimulated and the extent to which NKT cell responses can be controlled. These novel ligands are currently being evaluated in animal models of colitis. Here, we discuss strategies to alter NKT lymphocyte function in various settings and the potential clinical applications of natural glycolipids.