The acute phase response (APR) produces marked alterations in lipid and carbohydrate metabolism including decreasing plasma ketone levels. Fibroblast growth factor 21 (FGF21) is a recently discovered hormone that regulates lipid and glucose metabolism and stimulates ketogenesis. Here we demonstrate that lipopolysaccharide (LPS), zymosan, and turpentine, which induce the APR, increase serum FGF21 levels 2-fold. Although LPS, zymosan, and turpentine decrease the hepatic expression of FGF21, they increase FGF21 expression in adipose tissue and muscle, suggesting that extrahepatic tissues account for the increase in serum FGF21. After LPS administration, the characteristic decrease in plasma ketone levels is accentuated in FGF21-/- mice, but this is not due to differences in expression of carnitine palmitoyltransferase 1α or hydroxymethyglutaryl-CoA synthase 2 in liver, because LPS induces similar decreases in the expression of these genes in FGF21-/- and control mice. However, in FGF21-/- mice, the ability of LPS to increase plasma free fatty acid levels is blunted. This failure to increase plasma free fatty acid could contribute to the accentuated decrease in plasma ketone levels because the transport of fatty acids from adipose tissue to liver provides the substrate for ketogenesis. Treatment with exogenous FGF21 reduced the number of animals that die and the rapidity of death after LPS administration in leptin-deficient ob/ob mice and to a lesser extent in control mice. FGF21 also protected from the toxic effects of cecal ligation and puncture-induced sepsis. Thus, FGF21 is a positive APR protein that protects animals from the toxic effects of LPS and sepsis.

Regulatory CD4+CD25+ T cells (Tregs) suppress autoimmune and inflammatory diseases through mechanisms that are only partly understood. Previous studies suggest that Tregs can suppress bacterially triggered intestinal inflammation and respond to LPS through TLRs with enhanced suppressive activity. In this study, we have used murine cecal ligation and puncture as a model of polymicrobial sepsis to explore the effects of adoptive transfer of Tregs on septic outcome. Adoptive transfer of in vitro-stimulated Tregs in both prevention and therapeutic modes significantly improved survival of cecal ligation and puncture mice. Furthermore, the effect was dependent on both the number of Tregs adoptively transferred and the presence of host T cells. Animals that received stimulated Tregs had significantly increased peritoneal mast cells and peritoneal TNF-α production. More importantly, adoptive transfer of in vitro-stimulated Tregs significantly improved bacterial clearance, which resulted in improved survival. Our results suggest a novel role for Tregs in sepsis.

Targeted disruption of death receptor (DR)6 results in enhanced CD4+ T cell expansion and T helper cell type 2 differentiation after stimulation. Similar to T cells, DR6 is expressed on resting B cells but is down-regulated upon activation. We examined DR6−/− B cell responses both in vitro and in vivo. In vitro, DR6−/− B cells undergo increased proliferation in response to anti–immunoglobulin M, anti-CD40, and lipopolysaccharide. This hyperproliferative response was due, at least in part, to both increased cell division and reduced cell apoptosis when compared with wild-type B cells. Consistent with these observations, increased nuclear levels and activity of nuclear factor κB transcription factor, c-Rel, and elevated Bcl-xl expression were observed in DR6−/− B cells upon stimulation. In addition, DR6−/− B cells exhibited higher surface levels of CD86 upon activation and were more effective as antigen-presenting cells in an allogeneic T cell proliferation response. DR6−/− mice exhibited enhanced germinal center formation and increased titers of immunoglobulins to T-dependent as well as T-independent type I and II antigens. This is the first demonstration of a regulatory role of DR6 in the activation and function of B cells.

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DR6 is a recently identified member of the TNFR family. In a previous study, we have shown that DR6 KO mice have enhanced CD4+ T cell proliferation and Th2 cytokine production. Acute graft-vs-host disease (GVHD) results from the activation and expansion of alloreactive donor T cells following bone marrow transplantation. In this article, we demonstrate that the transfer of donor T cells from DR6 KO mice into allogeneic recipient mice in a parent into an F1 model of acute GVHD results in a more rapid onset of GVHD with increased severity. Recipients of DR6 KO T cells exhibit earlier systemic symptoms of GVHD, more rapid weight loss, earlier histopathological organ damage in the thymus, spleen, and intestines, and earlier mortality. The rapid onset of GVHD in these mice may be attributable to the enhanced activation and expansion of DR6 KO CD4+ and CD8+ T cells. Our findings support the hypothesis that DR6 serves as an important regulatory molecule in T cell immune responses. The identification and use of DR6 ligands and/or agonistic Abs to DR6 may represent useful therapeutics in the treatment of T cell-mediated diseases such as GVHD.