IFN-γ inhibits ovarian cancer progression via SOCS1/JAK/STAT signaling pathway.

PURPOSE: Ovarian cancer (OC) is a common malignancy, and IFN-γ, a multifunctional cytokine, is unveiled to impede the multiplication and enhance apoptosis in diverse tumor cells in previous research. Nonetheless, its function and mechanism in OC are blurred. METHODS: OC cell lines SKOV3 and OVCAR3 were dealt with different concentrations (0-40 ng/ml) of IFN-γ. CCK-8 experiment was utilized to examine cell multiplication; Flow cytometry was executed to detect apoptosis and cell cycle; Wound healing assay was utilized to detect cell migration; and Transwell experiment was implemented to examine cell invasion. qRT-PCR analysis was applied to detect STAT5, STAT3, JAK2 and JAK3 mRNA expression in OC cell lines. Western blot experiment was applied to detect the protein and phosphorylation levels of SOCS1, STAT5 and STAT3. RESULTS: IFN-γ suppressed OC cell multiplication in a concentration-dependent manner. Relative to the control group, IFN-γ restrained OC cell migration, invasion, enhanced apoptosis and prevented cell transformation from G0/G1 to S phase. Further analysis revealed that IFN-γ up-modulated SOCS1 expression and impeded STAT5 and STAT3 protein phosphorylation levels, and knockdown of SOCS1 partially counteracted the inhibitory effect of IFN-γ on STAT5 and STAT3 protein phosphorylation levels. CONCLUSION: IFN-γ represses OC progression by facilitating SOCS1 to suppress STAT3 and STAT5 protein phosphorylation.

SOCS1 Mediates Berberine-Induced Amelioration of Microglial Activated States in N9 Microglia Exposed to ß Amyloid.

Attenuating ß amyloid- (Aß-) induced microglial activation is considered to be effective in treating Alzheimer's disease (AD). Berberine (BBR) can reduce microglial activation in Aß-treated microglial cells; the mechanism, however, is still illusive. Silencing of cytokine signaling factor 1 (SOCS1) is the primary regulator of many cytokines involved in immune reactions, whose upregulation can reverse the activation of microglial cells. Microglia could be activated into two different statuses, classic activated state (M1 state) and alternative activated state (M2 state), and M1 state is harmful, but M2 is beneficial. In the present study, N9 microglial cells were exposed to Aß to imitate microglial activation in AD. And Western blot and immunocytochemistry were taken to observe inducible nitric oxide synthase (iNOS), Arginase-1 (Arg-1), and SOCS1 expressions, and the enzyme-linked immunosorbent assay (ELISA) was used to measure inflammatory and neurotrophic factor release. Compared with the normal cultured control cells, Aß exposure markedly increased the level of microglial M1 state markers (P < 0.05), including iNOS protein expression, tumor necrosis factor α (TNF-α), interleukin 1ß (IL-1ß), and IL-6 releases, and BBR administration upregulated SOSC1 expression and the level of microglial M2 state markers (P < 0.05), such as Arg-1 expression, brain-derived neurotrophic factor (BDNF), and glial cell-derived neurotrophic factor (GDNF) releases, downregulating the SOCS1 expression by using siRNA, however, significantly reversed the BBR-induced effects on microglial M1 and M2 state markers and SOCS1 expression (P < 0.05). These findings indicated that BBR can inhibit Aß-induced microglial activation via modulating the microglial M1/M2 activated state, and SOCS1 mediates the process.

Determinants of Ligand Specificity and Functional Plasticity in Type I Interferon Signaling.

The Type I Interferon family of cytokines all act through the same cell surface receptor and induce phosphorylation of the same subset of response regulators of the STAT family. Despite their shared receptor, different Type I Interferons have different functions during immune response to infection. In particular, they differ in the potency of their induced anti-viral and anti-proliferative responses in target cells. It remains not fully understood how these functional differences can arise in a ligand-specific manner both at the level of STAT phosphorylation and the downstream function. We use a minimal computational model of Type I Interferon signaling, focusing on Interferon-α and Interferon-ß. We validate the model with quantitative experimental data to identify the key determinants of specificity and functional plasticity in Type I Interferon signaling. We investigate different mechanisms of signal discrimination, and how multiple system components such as binding affinity, receptor expression levels and their variability, receptor internalization, short-term negative feedback by SOCS1 protein, and differential receptor expression play together to ensure ligand specificity on the level of STAT phosphorylation. Based on these results, we propose phenomenological functional mappings from STAT activation to downstream anti-viral and anti-proliferative activity to investigate differential signal processing steps downstream of STAT phosphorylation. We find that the negative feedback by the protein USP18, which enhances differences in signaling between Interferons via ligand-dependent refractoriness, can give rise to functional plasticity in Interferon-α and Interferon-ß signaling, and explore other factors that control functional plasticity. Beyond Type I Interferon signaling, our results have a broad applicability to questions of signaling specificity and functional plasticity in signaling systems with multiple ligands acting through a bottleneck of a small number of shared receptors.

Cyanocobalamin prevents cardiomyopathy in type 1 diabetes by modulating oxidative stress and DNMT-SOCS1/3-IGF-1 signaling.

Patients with long-standing diabetes have a high risk for cardiac complications that is exacerbated by increased reactive oxygen species (ROS) production. We found that feeding cyanocobalamin (B12), a scavenger of superoxide, not only prevented but reversed signs of cardiomyopathy in type 1 diabetic Elmo1H/H Ins2Akita/+ mice. ROS reductions in plasma and hearts were comparable to those in mice treated with other antioxidants, N-acetyl-L-cysteine or tempol, but B12 produced better cardioprotective effects. Diabetes markedly decreased plasma insulin-like growth factor (IGF)-1 levels, while B12, but not N-acetyl-L-cysteine nor tempol, restored them. B12 activated hepatic IGF-1 production via normalization of S-adenosylmethionine levels, DNA methyltransferase (DNMT)-1/3a/3b mRNA, and DNA methylation of promoters for suppressor of cytokine signaling (SOCS)-1/3. Reductions of cardiac IGF-1 mRNA and phosphorylated IGF-1 receptors were also restored. Thus, B12 is a promising option for preventing diabetic cardiomyopathy via ROS reduction and IGF-1 retrieval through DNMT-SOCS1/3 signaling.

Anti-inflammatory mechanisms of suppressors of cytokine signaling target ROS via NRF-2/thioredoxin induction and inflammasome activation in macrophages.

Suppressors of cytokine signaling (SOCS) exhibit diverse antiinflammatory effects. Since ROS acts as a critical mediator of inflammation, we have investigated the anti-inflammatory mechanisms of SOCS via ROS regulation in monocytic/macrophagic cells. Using PMA-differentiated monocytic cell lines and primary BMDMs transduced with SOCS1 or shSOCS1, the LPS/TLR4-induced inflammatory signaling was investigated by analyzing the levels of intracellular ROS, antioxidant factors, inflammasome activation, and pro-inflammatory cytokines. The levels of LPS-induced ROS and the production of pro-inflammatory cytokines were notably down-regulated by SOCS1 and up-regulated by shSOCS1 in an NAC-sensitive manner. SOCS1 up-regulated an ROS-scavenging protein, thioredoxin, via enhanced expression and binding of NRF-2 to the thioredoxin promoter. SOCS3 exhibited similar effects on NRF-2/thioredoxin induction, and ROS downregulation, resulting in the suppression of inflammatory cytokines. Notably thioredoxin ablation promoted NLRP3 inflammasome activation and restored the SOCS1-mediated inhibition of ROS and cytokine synthesis induced by LPS. The results demonstrate that the anti-inflammatory mechanisms of SOCS1 and SOCS3 in macrophages are mediated via NRF-2-mediated thioredoxin upregulation resulting in the downregulation of ROS signal. Thus, our study supports the anti-oxidant role of SOCS1 and SOCS3 in the exquisite regulation of macrophage activation under oxidative stress. [BMB Reports 2020; 53(12): 640-645].

Rhinovirus-Induced SIRT-1 via TLR2 Regulates Subsequent Type I and Type III IFN Responses in Airway Epithelial Cells.

IFN responses to viral infection are necessary to establish intrinsic antiviral state, but if unchecked can lead to heightened inflammation. Recently, we showed that TLR2 activation contributes to limitation of rhinovirus (RV)-induced IFN response in the airway epithelial cells. We also demonstrated that compared with normal airway epithelial cells, those from patients with chronic obstructive pulmonary disease (COPD) show higher IFN responses to RV, but the underlying mechanisms are not known. Initially, RV-induced IFN responses depend on dsRNA receptor activation and then are amplified via IFN-stimulated activation of JAK/STAT signaling. In this study, we show that in normal cells, TLR2 limits RV-induced IFN responses by attenuating STAT1 and STAT2 phosphorylation and this was associated with TLR2-dependent SIRT-1 expression. Further, inhibition of SIRT-1 enhanced RV-induced IFN responses, and this was accompanied by increased STAT1/STAT2 phosphorylation, indicating that TLR2 may limit RV-induced IFN responses via SIRT-1. COPD airway epithelial cells showed attenuated IL-8 responses to TLR2 agonist despite expressing TLR2 similar to normal, indicating dysregulation in TLR2 signaling pathway. Unlike normal, COPD cells failed to show RV-induced TLR2-dependent SIRT-1 expression. Pretreatment with quercetin, which increases SIRT-1 expression, normalized RV-induced IFN levels in COPD airway epithelial cells. Inhibition of SIRT-1 in quercetin-pretreated COPD cells abolished the normalizing effects of quercetin on RV-induced IFN expression in these cells, confirming that quercetin exerts its effect via SIRT-1. In summary, we show that TLR2 is required for limiting RV-induced IFNs, and this pathway is dysregulated in COPD airway epithelial cells, leading to exaggerated IFN production.

Deleting Suppressor of Cytokine Signaling-3 in chondrocytes reduces bone growth by disrupting mitogen-activated protein kinase signaling.

OBJECTIVE: To investigate the impact of deleting Suppressor of Cytokine Signaling (SOCS)-3 (SOCS3) in chondrocytes during murine skeletal development. METHOD: Mice with a conditional Socs3 allele (Socs3fl/fl) were crossed with a transgenic mouse expressing Cre recombinase under the control of the type II collagen promoter (Col2a1) to generate Socs3Δ/Δcol2 mice. Skeletal growth was analyzed over the lifespan of Socs3Δ/Δcol2 mice and controls by detailed histomorphology. Bone size and cortical bone development was evaluated by micro-computed tomography (micro-CT). Growth plate (GP) zone width, chondrocyte proliferation and apoptosis were assessed by immunofluorescence staining for Ki67 and TUNEL. Fibroblast growth factor receptor-3 (FGFR3) signaling in the GP was assessed by immunohistochemistry, while the effect of SOCS3 overexpression on FGFR3-driven pMAPK signaling in HEK293T cells was evaluated by Western blot. RESULTS: Socs3Δ/Δcol2 mice of both sexes were consistently smaller compared to littermate controls throughout life. This phenotype was due to reduced long bone size, poor cortical bone development, reduced Ki67+ proliferative chondrocytes and decreased proliferative zone (PZ) width in the GP. Expression of pMAPK, but not pSTAT3, was increased in the GPs of Socs3Δ/Δcol2 mice relative to littermate controls. Overexpression of FGFR3 in HEK293T cells increased Fibroblast Growth Factor 18 (FGF18)-dependent Mitogen-activated protein kinase (MAPK) phosphorylation, while concomitant expression of SOCS3 reduced FGFR3 expression and abrogated MAPK signaling. CONCLUSION: Our results suggest a potential role for SOCS3 in GP chondrocyte proliferation by regulating FGFR3-dependent MAPK signaling in response to FGF18.

Targeting Interleukin-6 Signaling in Clinic.

Interleukin-6 (IL-6) is a pleiotropic cytokine with roles in immunity, tissue regeneration, and metabolism. Rapid production of IL-6 contributes to host defense during infection and tissue injury, but excessive synthesis of IL-6 and dysregulation of IL-6 receptor signaling is involved in disease pathology. Therapeutic agents targeting the IL-6 axis are effective in rheumatoid arthritis, and applications are being extended to other settings of acute and chronic inflammation. Recent studies reveal that selective blockade of different modes of IL-6 receptor signaling has different outcomes on disease pathology, suggesting novel strategies for therapeutic intervention. However, some inflammatory diseases do not seem to respond to IL-6 blockade. Here, we review the current state of IL-6-targeting approaches in the clinic and discuss how to apply the growing understanding of the immunobiology of IL-6 to clinical decisions.

Isoflurane preconditioning ameliorates electromagnetic pulse-induced neural damage by shifting microglia polarization toward anti-inflammatory phenotype via upregulation of SOCS1.

With the speedy technological advances during the past few decades, human exposure to the electromagnetic field (EMF) has become increasingly common. Exposure to EMF may induce neural injuries and dysfunction of various organs, likely involving neuroinflammation and activation of microglial cells. Isoflurane preconditioning (IP) is shown to provide neuroprotection in various neurological diseases by inhibiting excessive neuroinflammatory responses. Brain samples harvested from rats exposed to electromagnetic pulse (EMP) with or without IP were subjected to qPCR, Western blot assay, and immunohistochemistry to determine the expression of pro-inflammatory/anti-inflammatory microglia markers and a variety of pro- and anti-inflammatory mediators. Suppressor of cytokine signaling 1 (SOCS1) siRNA was used in cultured N9 microglia cells to examine the roles of SOCS1 in the effect of IP. In both in vivo and in vitro experiments, EMP-exposed microglia were predominantly pro-inflammatory microglia, accompanied by increased expression of pro-inflammatory cytokines and chemokines, and activation of TLR4 pathway, leading to neuronal death. IP reversed the changes induced by EMP and switched the activated microglia to an anti-inflammatory phenotype. SOCS1 siRNA abolished the beneficial effects of IP. IP ameliorates EMP-induced neural injuries by shifting microglia polarization from pro-inflammatory to anti-inflammatory phenotype via upregulation of SOCS1.

SOCS1-targeted therapy ameliorates renal and vascular oxidative stress in diabetes via STAT1 and PI3K inhibition.

Oxidative stress resulting from excessive production of reactive oxygen species (ROS) or impaired antioxidant defenses is closely related to the development of diabetic vascular complications, including nephropathy and atherosclerosis. Chronic activation of Janus kinase/Signal transducer and activator of transcription (JAK/STAT) signaling pathway contributes to diabetic complications by inducing expression of genes involved in cell proliferation, fibrosis, inflammation, and oxidative stress. Suppressors of cytokine signaling (SOCS) family of endogenous JAK/STAT regulators is an attractive target for therapeutic intervention. We investigated the beneficial effect of two different SOCS1-targeted therapies (adenovirus-mediated gene transfer and kinase-inhibitory region peptidomimetic) to combat oxidative stress injury in an experimental diabetes model of concomitant renal and macrovascular disease (streptozotocin-induced diabetic apolipoprotein E-deficient mouse). Diabetes resulted in progressive alteration of redox balance in mice, as demonstrated by increased ROS levels and decreased antioxidant activity, which ultimately led to renal dysfunction and vascular injury. The molecular and pathological alterations in early diabetes were partially reversed by preventive intervention with SOCS1-targeted therapies. Importantly, SOCS1 peptidomimetic provided reno- and atheroprotection in diabetic mice even in a setting of established disease. Compared with untreated controls, kidney and aorta from SOCS1-treated mice exhibited significantly lower levels of superoxide anion, DNA oxidation marker and NADPH oxidase (Nox) subunits, along with higher expression of antioxidant enzymes. These trends correlated with a reduction in parameters of renal damage (albuminuria, creatinine and tubular injury), atherosclerosis (lesion size) and inflammation (leukocytes and chemokines). Mechanistic studies in renal, vascular and phagocytic cells exposed to cytokines and high-glucose showed that SOCS1 blocked ROS generation by inhibiting both Nox complex assembly and Nox subunit expression, an effect mediated by inactivation of JAK2, STAT1, and PI3K signaling pathways. This study provides evidence for SOCS1-targeted therapies, especially SOCS1 peptidomimetic, as an alternative antioxidant strategy to limit the progression of diabetic micro- and macrovascular complications.

miR-221-5p enhances cell proliferation and metastasis through post-transcriptional regulation of SOCS1 in human prostate cancer.

BACKGROUND: To investigate the effect of miR-221-5p on cell proliferaton and metastasis of human prostate cancer in vitro and vivo. METHODS: We established PC3 cell lines with stable overexpression or silencing of miRNA-221-5p via lentivirus infection. miRNA-221-5p and its target gene SOCS1 expression levels in the stable cells were analyzed by real-time polymerase chain reaction (RT-PCR) and western blotting. Using luciferase reporter assays to study the relationship between miR-221-5p and SOCS1. Cell proliferative activity was measured using the MTT assay and colony formation assay. Migration ability was assessed using wound-healing assay and transwell assay. To further study the function of miR-221-5p in human prostate cancer we established nude mice xenograft model in vivo. RESULTS: miR-221-5p regulates the proliferation, migration of prostate cancer cells in vitro and tumorigenesis in vivo by regulating socs1 expression through targeted its 3'UTR, and miR-221-5p regulates MAPK/ERK signaling pathway and EMT features in prostate cancer cells. CONCLUSIONS: Up-regulation and silencing of miR-221-5p expression in prostate cancer cells are correlated with cell proliferation, migration and tumorigenesis, which suggest that miR-221-5p plays an important role in prostate cancer progression.

SOCS-1 ameliorates smoke inhalation-induced acute lung injury through inhibition of ASK-1 activity and DISC formation.

Smoke inhalation leads to acute lung injury (ALI), a devastating clinical problem associated with high mortality. Suppressor of cytokine signaling-1 (SOCS-1) is a negative regulator of apoptosis and pro-inflammatory cytokine signaling, two major contributors to the pathogenesis of ALI. We have found that SOCS-1 protects lung epithelial cells from smoke-induced apoptosis through two mechanisms. One is that SOCS-1 enhances degradation of ASK-1 and diminishes cleavage of pro-caspase-3 to repress smoke-triggered apoptosis in lung epithelial cells. The other is that SOCS-1 represses smoke-triggered DISC formation through altering TRADD-caspase-8 interaction rather than TNFR-1-TRADD interaction or TNFR-1-TRAF-2 interaction. In conclusion, SOCS-1 relieves smoke inhalation-induced lung injury by repressing ASK-1 and DISC-mediated epithelium apoptosis.

SOCS1: Regulator of T Cells in Autoimmunity and Cancer.

SOCS1 is a negative feedback regulator of cytokine and growth factor receptor signaling, and plays an indispensable role in attenuating interferon gamma signaling. Studies on SOCS1-deficient mice have established a crucial role for SOCS1 in regulating CD8+ T cell homeostasis. In the thymus, SOCS1 prevents thymocytes that had failed positive selection from surviving and expanding, ensures negative selection and prevents inappropriate developmental skewing toward the CD8 lineage. In the periphery, SOCS1 not only controls production of T cell stimulatory cytokines but also attenuates the sensitivity of CD8+ T cells to synergistic cytokine stimulation and antigen non-specific activation. As cytokine stimulation of CD8+ T lymphocytes increases their sensitivity to low affinity TCR ligands, SOCS1 likely contributes to peripheral T cell tolerance by putting brakes on aberrant T cell activation driven by inflammatory cytokines. In addition, SOCS1 is critical to maintain the stability of T regulatory cells and control their plasticity to become pathogenic Th17 and Th1 cells under the harmful influence of inflammatory cytokines. SOCS1 also regulates T cell activation by dendritic cells via modulating their generation, maturation, antigen presentation, costimulatory signaling, and cytokine production. The above control mechanisms of SOCS1 on T cells, T regulatory cells and dendritic cells collectively contribute to immunological tolerance and prevent autoimmune manifestation. On other hand, silencing SOCS1 in dendritic cells or CD8+ T cells stimulates efficient antitumor immunity. Thus, even though SOCS1 is not a cell surface checkpoint inhibitor, its regulatory functions on T cell responses qualify SOCS1as a "non-classical" checkpoint blocker. SOCS1 also functions as a tumor suppressor in cancer cells by regulating oncogenic signal transduction pathways. The loss of SOCS1 expression observed in many tumors may have an impact on classical checkpoint pathways. The potential to exploit SOCS1 to treat inflammatory/autoimmune diseases and elicit antitumor immunity is discussed.

Daily Socs1 rhythms alter with aging differentially in peripheral clocks in male Wistar rats: therapeutic effects of melatonin.

Suprachiasmatic nucleus (SCN) in synchronization with the peripheral clocks regulates the temporal oscillations leading to overt rhythms. Aging leads to attenuation of such circadian regulation, accompanied by increased inflammatory mediators prevalently the cytokines. Suppressors of cytokine signaling (SOCS) family of proteins such as SOCS 1, 3 and cytokine-inducible SH2-containing protein (CIS) negatively regulate the cytokine signaling pathway. The role of SOCS1 in aging and circadian system is obscure. We therefore studied the daily rhythms of rSocs1 mRNA expression at Zeitgeber time (ZT) -0, 6, 12 and 18 in peripheral clocks such as liver, kidney, intestine and heart of 3, 12 and 24 months (m) old male Wistar rats. Interestingly the peripheral clocks studied displayed a rhythmic rSocs1 gene expression in 3 months. In 12 months group, 12 h phase advance in liver and 12 h phase delay in kidney and heart was observed with abolition of rhythms in intestine. Aging (24 months group) resulted in a phase advance by 6 h in liver and heart with abolition of rhythms in intestine in 24 months group. Kidney was also significantly affected upon aging with significant decrease in the rSocs1 levels and abolition of rhythms. The decrease in melatonin levels with aging is associated with decreased immunity and increased oxidative stress. The exogenous administration of melatonin has been linked to play a role in re-synchronization of circadian rhythms, reducing oxidative stress and enhancing immune properties. We therefore had studied the effect of exogenous melatonin upon age induced changes in daily rSocs1 gene expression patterns. Melatonin treatment partially restored the rhythms and daily pulse (ratio of maximum:minimum levels) in liver and intestine in 12 months group. Melatonin administration resulted in a significant increase in mean 24 h rSocs1 expression in intestine and heart of 24 months group compared to that of 3 months. The melatonin administration resulted in differential restoration of rSocs1 rhythms and levels in various tissues of 24 months old group. The sensitivity of 24 months old animals to melatonin found in the present study is a step towards endorsing melatonin as an important anti-aging therapeutic drug.

Suppressor of Cytokine Signaling-1 Peptidomimetic Limits Progression of Diabetic Nephropathy.

Diabetes is the main cause of CKD and ESRD worldwide. Chronic activation of Janus kinase and signal transducer and activator of transcription (STAT) signaling contributes to diabetic nephropathy by inducing genes involved in leukocyte infiltration, cell proliferation, and extracellular matrix accumulation. This study examined whether a cell-permeable peptide mimicking the kinase-inhibitory region of suppressor of cytokine signaling-1 (SOCS1) regulatory protein protects against nephropathy by suppressing STAT-mediated cell responses to diabetic conditions. In a mouse model combining hyperglycemia and hypercholesterolemia (streptozotocin diabetic, apoE-deficient mice), renal STAT activation status correlated with the severity of nephropathy. Notably, compared with administration of vehicle or mutant inactive peptide, administration of the SOCS1 peptidomimetic at either early or advanced stages of diabetes ameliorated STAT activity and resulted in reduced serum creatinine level, albuminuria, and renal histologic changes (mesangial expansion, tubular injury, and fibrosis) over time. Mice treated with the SOCS1 peptidomimetic also exhibited reduced kidney leukocyte recruitment (T lymphocytes and classic M1 proinflammatory macrophages) and decreased expression levels of proinflammatory and profibrotic markers that were independent of glycemic and lipid changes. In vitro, internalized peptide suppressed STAT activation and target gene expression induced by inflammatory and hyperglycemic conditions, reduced migration and proliferation in mesangial and tubuloepithelial cells, and altered the expression of cytokine-induced macrophage polarization markers. In conclusion, our study identifies SOCS1 mimicking as a feasible therapeutic strategy to halt the onset and progression of renal inflammation and fibrosis in diabetic kidney disease.

Effector T cell function rather than survival determines extent and duration of hepatitis in mice.

BACKGROUND & AIMS: Acute hepatitis is often mediated by cytotoxic T lymphocytes (CTLs); however, the intrinsic parameters that limit CTL-mediated liver injury are not well understood. METHODS: To investigate whether acute liver damage is limited by molecules that decrease the lifespan or effector function of CTLs, we used a well-characterized transgenic (Tg) mouse model in which acute liver damage develops upon transfer of T cell receptor (TCR) Tg CD8 T cells. Recipient Tg mice received donor TCR Tg T cells deficient for either the pro-apoptotic molecule Bim, which regulates CTL survival, or suppressor of cytokine signaling-1 (SOCS-1), which controls expression of common gamma chain cytokines; the effects of anti-PD-L1 neutralizing antibodies were also assessed. RESULTS: Use of Bim-deficient donor T cells and/or PD-L1 blockade increased the number of intrahepatic T cells without affecting the degree and kinetic of acute hepatitis. In contrast, SOCS-1-deficient T cells induced a heightened, prolonged acute hepatitis caused by their enhanced cytotoxic function and increased expansion. Although they inflicted more severe acute liver damage, SOCS-1-deficient T cells never precipitated chronic hepatitis and became exhausted. CONCLUSIONS: The degree of acute hepatitis is regulated by the function of CD8 T cells, but is not affected by changes in CTL lifespan. Although manipulation of the examined parameters affected acute hepatitis, persistent hepatitis did not ensue, indicating that, in the presence of high intrahepatic antigen load, changes in these factors in isolation were not sufficient to prevent T cell exhaustion and mediate progression to chronic hepatitis.