Hepatocellular carcinoma (HCC), the fastest rising cancer in the United States and increasing in Europe, often occurs with nonalcoholic steatohepatitis (NASH). Mechanisms underlying NASH and NASH-induced HCC are largely unknown. We developed a mouse model recapitulating key features of human metabolic syndrome, NASH, and HCC by long-term feeding of a choline-deficient high-fat diet. This induced activated intrahepatic CD8(+) T cells, NKT cells, and inflammatory cytokines, similar to NASH patients. CD8(+) T cells and NKT cells but not myeloid cells promote NASH and HCC through interactions with hepatocytes. NKT cells primarily cause steatosis via secreted LIGHT, while CD8(+) and NKT cells cooperatively induce liver damage. Hepatocellular LTβR and canonical NF-κB signaling facilitate NASH-to-HCC transition, demonstrating that distinct molecular mechanisms determine NASH and HCC development.

CD95 (also called Fas and APO-1) is a prototypical death receptor that regulates tissue homeostasis mainly in the immune system through induction of apoptosis 1-3. During cancer progression CD95 is frequently downregulated or cells are rendered apoptosis resistant 4,5 raising the possibility that loss of CD95 is part of a mechanism for tumour evasion. However, complete loss of CD95 is rarely seen in human cancers 4 and many cancer cells express large quantities of CD95 and are highly sensitive to CD95 mediated apoptosis in vitro. Furthermore, cancer patients frequently have elevated levels of the physiological ligand for CD95, CD95L 6. These data raise the intriguing possibility that CD95 could actually promote the growth of tumours through its nonapoptotic activities 7. Here we show that cancer cells in general, regardless of their CD95 apoptosis sensitivity, depend on constitutive activity of CD95, stimulated by cancer-produced CD95L, for optimal growth. Consistently, loss of CD95 in mouse models of ovarian cancer and liver cancer reduces cancer incidence as well as the size of the tumours. The tumorigenic activity of CD95 is mediated by a pathway involving JNK and c-Jun. These results demonstrate that CD95 plays a growth promoting role during tumorigenesis and suggest that efforts to inhibit its activity rather than to enhance its activation should be considered during cancer therapy.

Tumor necrosis factor (TNF, TNFalpha) is implicated in various pathophysiological processes and can be either protective, as in host defense, or deleterious, as in autoimmunity or toxic shock. To uncover the in vivo functions of TNF produced by different cell types, we generated mice with TNF ablation targeted to various leukocyte subsets. Systemic TNF in response to lipopolysaccharide was produced mainly by macrophages and neutrophils. This source of TNF was indispensable for resistance to an intracellular pathogen, Listeria, whereas T-cell-derived TNF was important for protection against high bacterial load. Additionally, both T-cell-derived TNF and macrophage-derived TNF had critical and nonredundant functions in the promotion of autoimmune hepatitis. Our data suggest that T-cell-specific TNF ablation may provide a therapeutic advantage over systemic blockade.

Amyloid beta (Abeta) is a major contributor to the pathogenesis of Alzheimer's disease (AD). Although Abeta has been reported to be directly neurotoxic, it also causes indirect neuronal damage by activating mononuclear phagocytes (microglia) that accumulate in and around senile plaques. In this study, we show that the 42 amino acid form of beta amyloid peptide, Abeta(42), is a chemotactic agonist for a seven-transmembrane, G-protein-coupled receptor named FPR-Like-1 (FPRL1), which is expressed on human mononuclear phagocytes. Moreover, FPRL1 is expressed at high levels by inflammatory cells infiltrating senile plaques in brain tissues from AD patients. Thus, FPRL1 may mediate inflammation seen in AD and is a potential target for developing therapeutic agents.

In order to definitively ascertain the functional contribution of lymphotoxin (LT) expressed by B cells, we produced mice with the LTbeta gene deleted from B cells (B-LTbeta KO mice). In contrast to systemic LTbeta deletion, in B-LTbeta KO mice only splenic microarchitecture was affected, while lymph nodes and Peyer's patches (PP) were normal, except for PP's reduced size. Even though B-LTbeta KO spleens retained a small number of follicular dendritic cells (FDC) which appeared to be dependent on LTbeta produced by T cells, IgG responses to sheep red blood cells were markedly reduced. Thus, the organogenic function of B-LTbeta is almost entirely restricted to spleen, where it supports the correct lymphoid architecture that is critical for an effective humoral immune response.

Immunoglobulin A (IgA) production at mucosal surfaces contributes to protection against pathogens and controls intestinal microbiota composition. However, mechanisms regulating IgA induction are not completely defined. We show that soluble lymphotoxin α (sLTα3) produced by RORγt(+) innate lymphoid cells (ILCs) controls T cell-dependent IgA induction in the lamina propria via regulation of T cell homing to the gut. By contrast, membrane-bound lymphotoxin β (LTα1β2) produced by RORγt(+) ILCs is critical for T cell-independent IgA induction in the lamina propria via control of dendritic cell functions. Ablation of LTα in RORγt(+) cells abrogated IgA production in the gut and altered microbiota composition. Thus, soluble and membrane-bound lymphotoxins produced by ILCs distinctly organize adaptive immune responses in the gut and control commensal microbiota composition.

Summary Innate lymphoid cells (ILCs) have emerged as important players regulating the balance between protective immunity and immunopathology at mucosal surfaces. However, mechanisms that regulate ILCs effector functions during mucosal pathogenic challenge are poorly defined. Using mice infected with the natural mouse enteric pathogen Citrobacter rodentium, we demonstrate that lymphotoxin (LT) is essential for IL-22 production by intestinal ILCs. Blocking of LTβR signaling dramatically reduced intestinal IL-22 production after C. rodentium infection. Conversely, stimulating LTβR signaling induced IL-22 protection pathway in LT-deficient mice. Furthermore, exogenous IL-22 expression rescued LTβR deficient mice. IL-22 producing ILCs were predominantly located in lymphoid follicles in the colon, and interacted closely with dendritic cells. Finally, we find that an LT-driven positive feedback loop controls IL-22 production by RORγt+ ILCs via LTβR signaling in dendritic cells. Altogether, we show that LTβR signaling in gut lymphoid follicles regulates IL-22 production by ILCs in response to mucosal pathogen challenge.

SUMMARY Neutralizing antibodies have been thought to be required for protection against acutely cytopathic viruses, such as the neurotropic vesicular stomatitis virus (VSV). Utilizing mice that possess B cells but lack antibodies, we show here that survival upon subcutaneous (s.c.) VSV challenge was independent of neutralizing antibody production or cell-mediated adaptive immunity. However, B cells were absolutely required to provide lymphotoxin (LT) α1β2, which maintained a protective subcapsular sinus (SCS) macrophage phenotype within virus draining lymph nodes (LNs). Macrophages within the SCS of B cell-deficient LNs, or of mice that lack LTα1β2 selectively in B cells, displayed an aberrant phenotype, failed to replicate VSV, and therefore did not produce type I interferons, which were required to prevent fatal VSV invasion of intranodal nerves. Thus, although B cells are essential for survival during VSV infection, their contribution involves the provision of innate differentiation and maintenance signals to macrophages, rather than adaptive immune mechanisms.