Interferon‐γ constrains cytokine production of group 2 innate lymphoid cells

Group 2 innate lymphoid cells (ILC2s) produce a significant amount of interleukin‐5 (IL‐5), which supports eosinophil responses in various tissues; they also produce IL‐13, which induces mucus production and contributes to tissue repair or fibrosis. The ILC2s are activated by alarmins, such as IL‐33 released from epithelia, macrophages and natural killer T (NKT) cells in response to infection and allergen exposure, leading to epithelial injury. We examined gene expression in lung ILC2s and found that ILC2s expressed Ifngr1, the receptor for interferon‐γ (IFN‐γ). Interferon‐γ severely inhibited IL‐5 and IL‐13 production by lung and kidney ILC2s. To evaluate the effects in vivo, we used α‐galactosylceramide (α‐GalCer) to induce NKT cells to produce IL‐33 and IFN‐γ. Intraperitoneal injection of α‐GalCer in mice induced NKT cell activation resulting in IL‐5 and IL‐13 production by ILC2s. Administration of anti‐IFN‐γ together with α‐GalCer significantly enhanced the production of IL‐5 and IL‐13 by ILC2s in lung and kidney. Conversely, cytokine production from ILC2s was markedly suppressed after injection of exogenous IL‐33 in Il33^?/? mice pre‐treated with α‐GalCer. Hence, IFN‐γ induced or already present in tissues can impact downstream pleiotropic functions mediated by ILC2s, such as inflammation and tissue repair.     

Suppression of murine tumour growth through CD8+ cytotoxic T lymphocytes via activated DEC‐205+ dendritic cells by sequential administration of α‐galactosylceramide in vivo

Cancer immunity is mediated through the effective priming and activation of tumour‐specific class I MHC molecule‐restricted CD8⁺ cytotoxic T lymphocytes (CTLs). DEC‐205⁺ dendritic cells (DCs) can cross‐present the epitope(s) of captured tumour antigens associated with class I MHC molecules alongside co‐stimulatory molecules to prime and activate tumour‐specific CD8⁺ CTLs. Immunosuppressive tolerogenic DCs with reduced co‐stimulatory molecules may be a cause of impaired CTL induction. Hepa1‐6‐1 cells were established from the mouse hepatoma cell line Hepa1‐6; these cells grow continuously after subcutaneous implantation into syngeneic C57BL/6 (B6) mice and do not prime CD8⁺ CTLs. In this study, we show that the growth of ongoing tumours was suppressed by activated CD8⁺ CTLs with tumour‐specific cytotoxicity through the administration of the glycolipid α‐galactosylceramide (α‐GalCer), which is a compound known to stimulate invariant natural killer T (iNKT) cells and selectively activate DEC‐205⁺ DCs. Moreover, we demonstrated that sequential repetitive intraperitoneal inoculation with α‐GalCer every 48 hr appeared to convert tolerogenic DEC‐205⁺ DCs into immunogenic DCs with a higher expression of co‐stimulatory molecules and a stronger cross‐presentation capacity, which primed CTL precursors and induced tumour‐specific CD8⁺ CTLs within the tumour environment without activating iNKT cells. These findings provide a new basis for cancer immunotherapy to convert tolerogenic DEC‐205⁺ DCs within tumours into immunogenic DCs through the sequential administration of an immuno‐potent lipid/glycolipid, and then activated immunogenic DCs with sufficient expression of co‐stimulatory molecules prime and activate tumour‐specific CD8⁺ CTLs within the tumour to control tumour growth.     

Activation of invariant natural killer T cells in regional lymph nodes as new antigen‐specific immunotherapy via induction of interleukin‐21 and interferon‐γ

Invariant natural killer T (iNKT) cells play important immunoregulatory functions in allergen‐induced airway hyperresponsiveness and inflammation. To clarify the role of iNKT cells in allergic rhinitis (AR), we generated bone marrow‐derived dendritic cells (BMDCs), which were pulsed by ovalbumin (OVA) and α‐galactosylceramide (OVA/α‐GalCer‐BMDCs) and administered into the oral submucosa of OVA‐sensitized mice before nasal challenge. Nasal symptoms, level of OVA‐specific immunoglobulin (IgE), and T helper type 2 (Th2) cytokine production in cervical lymph nodes (CLNs) were significantly ameliorated in wild‐type (WT) mice treated with OVA/α‐GalCer‐BMDCs, but not in WT mice treated with OVA‐BMDCs. These anti‐allergic effects were not observed in Jα18^–/– recipients that lack iNKT cells, even after similar treatment with OVA/α‐GalCer‐BMDCs in an adoptive transfer study with CD4⁺ T cells and B cells from OVA‐sensitized WT mice. In WT recipients of OVA/α‐GalCer‐BMDCs, the number of interleukin (IL)‐21‐producing iNKT cells increased significantly and the Th1/Th2 balance shifted towards the Th1 dominant state. Treatment with anti‐IL‐21 and anti‐interferon (IFN)‐γ antibodies abrogated these anti‐allergic effects in mice treated with α‐GalCer/OVA‐BMDCs. These results suggest that activation of iNKT cells in regional lymph nodes induces anti‐allergic effects through production of IL‐21 or IFN‐γ, and that these effects are enhanced by simultaneous stimulation with antigen. Thus, iNKT cells might be a useful target in development of new treatment strategies for AR.     

Feedback regulation of IFN‐α/β signaling by Axl receptor tyrosine kinase modulates HBV immunity

Hepatitis B virus (HBV) is known to cause age‐dependent infection outcomes wherein most infections during young age result in chronicity. The mechanism underlying the differential outcome remains elusive. By using hydrodynamic injection of the replication‐competent pAAV‐HBV, we established a mouse model in which HBV persistence was generated in 4–5 w/o C57BL/6 young mice, but not in adult mice over 10 w/o. HBV‐tolerant young mice expressed higher interferon (IFN)‐α/β levels in hepatocytes and intrahepatic plasmacytoid DCs (pDCs) than adult mice after pAAV‐HBV injection. Excessive IFN‐α/β expression in young mice was associated with induction of the Axl regulatory pathway and expansion of intrahepatic Treg cells. In line with these findings, augmented IFN‐β expression increased Axl expression in the liver and HBV persistence in adult mice, whereas IFN‐α/β signaling blockage decreased Axl expression and HBV persistence in young mice. Accordingly, Axl overexpression decreased HBV clearance of adult mice whereas Axl silencing enhanced HBV clearance of young mice. In vitro, IFN‐β priming of pDCs and Axl‐overexpressing macrophages enhanced Treg‐cell differentiation. These findings suggest that age‐dependent HBV chronicity is attributed to IFN‐β‐Axl immune regulation, which is selectively induced in young mice by excessive IFN‐α/β production at early stage of HBV infection.     

α‐Galactosylceramide stimulates splenic lymphocyte proliferation in vitro and increases antibody production in vivo in late neonatal‐age mice

The neonatal stage is characterized by weak responses to various infections and vaccines, thus the development of efficient formulas to improve vaccine effectiveness is of high priority. The glycolipid alpha galactosylceramide (αGalCer) is known as a potent immune modulator due mainly to natural killer (NK) T cell activation. Using a mouse tetanus toxoid (TT) immunization model, we observed that neonatal mice given αGalCer at the time of primary immunization on postnatal day (pnd) 17 had a significantly higher TT‐specific immunoglobulin (Ig)M response as well as a memory IgG response, while αGalCer given on pnd 7 resulted in only marginal boosting. Consistently, immunostaining of the spleen sections from αGalCer‐treated pnd 17 immunized neonates showed a higher number of Ki67⁺ cells in the splenic germinal centre area, suggesting a stronger response after immunization. In‐vitro kinetic studies revealed that spleen cells from newborn to pnd 7 neonates did not respond to αGalCer stimulation, whereas cell proliferation was increased markedly by αGalCer after pnd 7, and became dramatic around neonatal pnd 17–18, which was accompanied by increased B, T and NK T cell populations in the spleen. In addition, in pnd 17 spleen cells, αGalCer significantly stimulated the production of NK T cytokines, interleukin (IL)‐4 and interferon (IFN)‐γ, and promoted the proliferation of CD23⁺ B cells, a subset of B cells enriched in germinal centres. These data suggest that αGalCer is an effective immune stimulus in the late neonatal stage, and thus may be useful in translational studies to test as a potential adjuvant to achieve a more efficient response to immunization.     

γδ T cells are indispensable for interleukin‐23‐mediated protection against Concanavalin A‐induced hepatitis in hepatitis B virus transgenic mice

Hepatitis B virus surface antigen (HBsAg) carriers are highly susceptible to liver injury triggered by environmental biochemical stimulation. Previously, we have reported an inverse correlation between γδ T cells and liver damage in patients with hepatitis B virus (HBV). However, whether γδ T cells play a role in regulating the hypersensitivity of HBsAg carriers to biochemical stimulation‐induced hepatitis is unknown. In this study, using HBV transgenic (HBs‐Tg) and HBs‐Tg T‐cell receptor‐δ‐deficient (TCR‐δ^−/−) mice, we found that mice genetically deficient in γδ T cells exhibited more severe liver damage upon Concanavalin A (Con A) treatment, as indicated by substantially higher serum alanine aminotransferase levels, further elevated interferon‐γ (IFN‐γ) levels and more extensive necrosis. γδ T‐cell deficiency resulted in elevated IFN‐γ in CD4⁺ T cells but not in natural killer or natural killer T cells. The depletion of CD4⁺ T cells and neutralization of IFN‐γ reduced liver damage in HBs‐Tg and HBs‐Tg‐TCR‐δ^−/− mice to a similar extent. Further investigation revealed that HBs‐Tg mice showed an enhanced interleukin‐17 (IL‐17) signature. The administration of exogenous IL‐23 enhanced IL‐17A production from Vγ4 γδ T cells and ameliorated liver damage in HBs‐Tg mice, but not in HBs‐Tg‐TCR‐δ^−/− mice. In summary, our results demonstrated that γδ T cells played a protective role in restraining Con A‐induced hepatitis by inhibiting IFN‐γ production from CD4⁺ T cells and are indispensable for IL‐23‐mediated protection against Con A‐induced hepatitis in HBs‐Tg mice. These results provided a potential therapeutic approach for treating the hypersensitivity of HBV carriers to biochemical stimulation‐induced liver damage.     

Leishmania donovani‐induced expression of signal regulatory protein α on Kupffer cells enhances hepatic invariant NKT‐cell activation

Signal regulatory protein α (SIRPα) and its cognate ligand CD47 have been documented to have a broad range of cellular functions in development and immunity. Here, we investigated the role of SIRPα–CD47 signalling in invariant NKT (iNKT) cell responses. We found that CD47 was required for the optimal production of IFN‐γ from splenic iNKT cells following exposure to the αGalCer analogue PBS‐57 and in vivo infection of mice with Leishmania donovani. Surprisingly, although SIRPα was undetectable in the liver of uninfected mice, the hepatic iNKT‐cell response to infection was also impaired in CD47^?/? mice. However, we found that SIRPα was rapidly induced on Kupffer cells following L. donovani infection, via a mechanism involving G‐protein‐coupled receptors. Thus, we describe a novel amplification pathway affecting cytokine production by hepatic iNKT cells, which may facilitate the breakdown of hepatic tolerance after infection.     

Immune Regulation by T Regulatory Cells in Hepatitis B Virus‐Related Inflammation and Cancer

Hepatocellular carcinoma (HCC) is the leading cause of cancer death, and hepatitis B virus (HBV) infection is one of the commonest causes in Asian countries. India has the second largest pool after China for hepatitis B‐infected subjects. HBV clearance is T cell dependent, and one of the reasons for T cells hyporesponsiveness is due to mass production of regulatory T cells (Tregs) through activation of Notch signalling, which suppress CD4/CD8 T cells. Tregs are important to maintain cellular homoeostasis; however, during viral infection increase of Tregs is inversely proportional to HBV DNA titres. Tregs exert their suppressive effect either via cell‐to‐cell contact or through release of interleukin (IL)‐2, IL‐10, TGF‐β and IL‐35. In Chronic hepatitis B virus CHBV infection, PD‐1 pathway also gets activated and is involved in promoting tolerance. However, with Tregs induction, virus‐specific T cell responses also get decreased. Circulatory and intratumoural Tregs promote development of HBV‐specific HCC more by decreasing and impairing the effector functions of CD8 T cells. Antiviral therapies and PD‐1 blockade strategy had shown the inhibition of Tregs and reduction in HBV DNA. However, inhibition of HBV‐specific Tregs is major challenge for future therapies. New cytokine blockade therapies have emerged as potential therapeutic potentials.     

In‐vivo stimulation of macaque natural killer T cells with α‐galactosylceramide

Natural killer T cells are a potent mediator of anti‐viral immunity in mice, but little is known about the effects of manipulating NKT cells in non‐human primates. We evaluated the delivery of the NKT cell ligand, α‐galactosylceramide (α‐GalCer), in 27 macaques by studying the effects of different dosing (1–100 μg), and delivery modes [directly intravenously (i.v.) or pulsed onto blood or peripheral blood mononuclear cells]. We found that peripheral NKT cells were depleted transiently from the periphery following α‐GalCer administration across all delivery modes, particularly in doses of ≥10 μg. Furthermore, NKT cell numbers frequently remained depressed at i.v. α‐GalCer doses of >10 μg. Levels of cytokine expression were also not enhanced after α‐GalCer delivery to macaques. To evaluate the effects of α‐GalCer administration on anti‐viral immunity, we administered α‐GalCer either together with live attenuated influenza virus infection or prior to simian immunodeficiency virus (SIV) infection of two macaques. There was no clear enhancement of influenza‐specific T or B cell immunity following α‐GalCer delivery. Further, there was no modulation of pathogenic SIV_mac251 infection following α‐GalCer delivery to a further two macaques in a pilot study. Accordingly, although macaque peripheral NKT cells are modulated by α‐GalCer in vivo, at least for the dosing regimens tested in this study, this does not appear to have a significant impact on anti‐viral immunity in macaque models.     

Significance of liver histology in HBsAg‐positive,IgM anti‐HBc‐negative acute hepatitis B virus‐related hepatitis

Delladetsima I, Papatheodoridis G V, Tiniakos D G, Hatzakis A & Tassopoulos N C
(2012) Histopathology  61, 881–888 Significance of liver histology in HBsAg‐positive, IgM anti‐HBc‐negative acute hepatitis B virus‐related hepatitis Aims: The natural course of HBsAg‐positive, IgM anti‐HBc‐negative acute hepatitis B virus (HBV)‐related hepatitis is unclear. The aim of this study was to evaluate the prognostic significance of histological features and hepatic expression of HBV antigens in such patients. Methods and results: Fifty patients with HBsAg‐positive, IgM anti‐HBc‐negative acute hepatitis B who underwent liver biopsy during the acute hepatitis episode were studied [HBeAg seroconversion (n = 16), persistently positive for HBeAg (n = 9), and persistently negative for HBeAg (n = 25)]. Twenty‐six cases had features of typical acute hepatitis only (group A), and 24 cases had changes suggesting pre‐existing chronic hepatitis (group B). HBcAg and/or HBsAg immunoreactivity was detected less frequently in group A than in group B (31% versus 79%, P = 0.01). HBsAg clearance was observed in 24% of patients, almost exclusively in cases with HBeAg seroconversion. HBsAg loss was significantly more frequent in group A than in group B (52% versus 0%, P < 0.001), and in cases without rather than with immunohistochemical expression of HBV antigens (55% versus 0%, P < 0.001). In group A, HBsAg clearance was observed in 80%, 54% and 0% of patients with mild, moderate or severe acute hepatitis, respectively (P = 0.034). Conclusions: Histological information is very important for the prognosis of HBsAg‐positive, IgM anti‐HBc‐negative acute hepatitis B. HBeAg seroconversion with underlying typical acute hepatitis changes of mild to moderate severity without hepatic expression of HBV antigens strongly predicts subsequent HBsAg loss.     

Expression of activation‐induced cytidine deaminase enhances the clearance of pneumococcal pneumonia: evidence of a subpopulation of protective anti‐pneumococcal B1a cells

We describe a protective early acquired immune response to pneumococcal pneumonia that is mediated by a subset of B1a cells. Mice deficient in B1 cells (xid), or activation‐induced cytidine deaminase (AID^?/?), or invariant natural killer T (iNKT) cells (Jα18^?/?), or interleukin‐13 (IL‐13^?/?) had impaired early clearance of pneumococci in the lung, compared with wild‐type mice. In contrast, AID^?/? mice adoptively transferred with AID^+/+ B1a cells, significantly cleared bacteria from the lungs as early as 3 days post infection. We show that this early bacterial clearance corresponds to an allergic contact sensitivity‐like cutaneous response, probably due to a subpopulation of initiating B1a cells. In the pneumonia model, these B1a cells were found to secrete higher affinity antigen‐specific IgM. In addition, as in contact sensitivity, iNKT cells were required for the anti‐pneumococcal B1a cell initiating response, probably through early production of IL‐13, given that IL‐13^?/? mice also failed to clear infection. Our study is the first to demonstrate the importance of AID in generating an appropriate B1a cell response to pathogenic bacteria. Given the antibody affinity and pneumonia resistance data, natural IgM produced by conventional B1a cells are not responsible for pneumonia clearance compared with the AID‐dependent subset.     

Role of Valpha14+ NKT cells in the development of Hepatitis B virus-specific CTL: activation of Valpha14+ NKT cells promotes the breakage of CTL tolerance

CTLs are thought to be major effectors for clearing viruses in acute infections including hepatitis B virus (HBV). Persistent HBV infection is characterized by a lack of or a weak CTL response to HBV, which is thought to reflect tolerance to HBV antigens. In the present study, we found that alpha-galactosylceramide (alpha-GalCer), a ligand for Valpha14-positive NKT cells, strongly enhanced the induction and proliferation of HBV-specific CTLs by HBsAg. In HBsAg transgenic mice, which are thought to be tolerant to HBV-encoded antigens, administration of HBsAg or alpha-GalCer alone failed to induce HBsAg-specific CTLs, but they were induced by co-administration of both compounds. Furthermore, by limiting dilution analysis, we confirmed the existence of HBsAg-specific CTL precursors in the HBsAg transgenic mice immunized with HBsAg and alpha-GalCer. A blocking experiment using antibodies to cytokines and CD40 ligand showed that IL-2 and CD40-CD40L interaction mediate the enhancement of CTL induction caused by alpha-GalCer through NKT cell activation. Our results may open up a new method for clearing the virus from patients with persistent HBV infection.     

α‐Galactosylceramide‐activated murine NK1.1+ invariant‐NKT cells in the myometrium induce miscarriages in mice

Innate immunity, which is unable to discriminate self from allo‐antigens, is thought to be important players in the induction of miscarriages. Here, we show that the administration of IL‐12 to syngeneic‐mated C57BL/6 mice on gestation day 7.5 (Gd 7.5), drives significant miscarriages in pregnant females. Furthermore, the administration on Gd 7.5 of α‐galactosylceramide (α‐GalCer), which is known to activate invariant natural killer T (iNKT) cells, induced miscarriages in both syngeneic‐mated C57BL/6 mice and allogeneic‐mated mice (C57BL/6 (♀) × BALB/c (♂)). Surprisingly, the percentages of both DEC‐205⁺ DCs and CD1d‐restricted NK1.1⁺ iNKT cells were higher in the myometrium of pregnant mice treated i.p. with α‐GalCer than in the decidua. IL‐12 secreted from α‐GalCer‐activated DEC‐205⁺ DCs stimulated the secretion of cytokines, including IL‐2, IL‐4, IFN‐γ, TNF‐α, perforin, and granzyme B, from the NK1.1⁺ iNKT cells in the myometrium, leading to fetal loss in pregnant mice. Finally, the i.p. administration of IL‐12 and/or α‐GalCer in iNKT‐deficient Jα18(‐/‐) (Jα18 KO) mice did not induce miscarriages. This study provides a new perspective on the importance of the myometrium, rather than the decidua, in regulating pregnancy and a mechanism of miscarriage mediated by activated DEC‐205⁺ DCs and NK1.1⁺ iNKT cells in the myometrium of pregnant mice.     

α‐GalCer ameliorates listeriosis by accelerating infiltration of Gr‐1+ cells into the liver

α‐Galactosylceramide (α‐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 α‐GalCer. Here, we show that α‐GalCer treatment ameliorates murine listeriosis, and inhibits inflammation following Listeria monocytogenes infection. Liver infiltration of Gr‐1⁺ cells and γ/δ T cells was accelerated by α‐GalCer treatment. Gr‐1⁺ cell and γ/δ T‐cell depletion exacerbated listeriosis in α‐GalCer‐treated mice, and this effect was more pronounced after depletion of Gr‐1⁺ cells than that of γ/δ T cells. Although GM‐CSF and IL‐17 were secreted by NKT cells after α‐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 α‐GalCer treatment, CD11b^?Gr‐1⁺ cells were numerically reduced in the bone marrow. In addition, respiratory burst in Gr‐1⁺ cells was enhanced by α‐GalCer treatment. Our results indicate that α‐GalCer‐induced antibacterial immunity is caused, in part, by accelerated infiltration of Gr‐1⁺ cells and to a lesser degree of γ/δ 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.     

Immunological tolerance to LCMV antigens differently affects control of acute and chronic virus infection in mice

Cytotoxic T lymphocytes (CTLs) play a key role in the control of lymphocytic choriomeningitis virus (LCMV) infection. In C57BL/6 mice (H‐2^b), the CTL response is mainly directed against epitopes from the LCMV glycoprotein (GP) and the nucleoprotein (NP) which represent the two major viral proteins. The role of GP‐ versus NP‐derived epitopes for viral clearance was examined using transgenic (tg) mice ubiquitously expressing LCMV GP and NP, respectively. These mice lack GP‐ or NP‐specific CTLs and show decreased levels of GP‐ or NP‐specific antibodies as a result of tolerance induction. During acute LCMV infection, CTLs specific for GP‐ and NP‐derived epitopes are generated with similar frequencies. Nonetheless, we found that lack of GP‐ but not of NP‐specific CTLs abolished control of acute LCMV infection. In contrast, after high‐dose or chronic LCMV infection, virus elimination was delayed to a similar extent in GP‐ and NP‐tg mice. Thus, immunological tolerance to LCMV antigens differently affects virus clearance in acute and chronic infection settings. In addition, our data reveal that immunodominance of H‐2^b‐restricted LCMV‐specific CTL epitopes and their antiviral activity do not strictly correlate.     

HBcAg‐Specific IL‐21‐Producing CD4+ T Cells are Associated with Relative Viral Control in Patients with Chronic Hepatitis B

Function exhaustion of specific cytotoxic CD8+ T cell in chronic virus infection partly results from the low levels of CD4 help, but the mechanisms by which CD4 help T cell required to control hepatitis B virus infection are not well understood. In this study, we investigated the role of interleukin‐21‐producing CD4+ T cell response in viral control of hepatitis B virus infection. HBcAg‐specific interleukin‐21‐producing CD4+ T cells in blood were detected in patients with hepatitis B virus infection. Patients with acute hepatitis B had greater HBcAg‐specific interleukin‐21‐producing CD4+ T cells in blood compared with chronic hepatitis B patients, and there was no statistical significance between immune active chronic hepatitis B patients and inactive healthy carrier patients for these cells, whereas frequencies of these cells negatively correlated with HBV DNA levels but positively correlated with HBc18‐27‐specific IFN‐γ‐producing CD8+ T cells. Moreover, interleukin‐21 sustained HBc18‐27‐specific CD8+ T cells in vitro, and interleukin‐21 production by HBcAg‐specific IL‐21‐producing CD4+ T cells of acute hepatitis B patients enhanced IFN‐γ and perforin expression by CD8+ T cells from chronic hepatitis B patients. Our results demonstrate that HBcAg‐specific interleukin‐21‐producing CD4+ T cell responses might contribute to viral control by sustaining CD8+ T cell antiviral function.     

Indolamine 2,3‐dioxygenase expression by monocytes and dendritic cell populations in hepatitis C patients

Dendritic cells (DCs) play an important role in the induction of the primary immune response to infection. DCs may express the tryptophan‐catabolizing enzyme indolamine2,3‐dioxygenase (IDO), which is an inducer of immune tolerance. Because there is evidence that chronic hepatitis C virus (HCV) infection leads to functional impairment of certain DC populations, we analysed IDO expression in DCs and monocytes from chronically infected and recovered HCV patients. The IDO1 and ‐2 expression was increased significantly in the monocytes of chronic HCV patients but, interestingly, not in those from recovered patients. The myeloid DCs from chronically infected HCV patients also showed enhanced IDO1 expression, while no change in either IDO1 or ‐2 was found for plasmacytoid DCs. Up‐regulation of IDO1 gene expression was confirmed by the presence of enhanced kynurenine/tryptophan ratios in the plasma from chronic HCV patients. Increased IDO1 and ‐2 expression was also observed in monocytes from healthy donors infected with an adapted mutant of the HCV JFH‐1 strain ex vivo, confirming a direct effect of HCV infection. These changes in IDO expression could be prevented by treatment with the IDO inhibitor 1‐methyl tryptophan (1‐mT). Furthermore, maturation of monocyte‐derived DCs from chronically infected HCV patients, as well as well as monocyte‐derived DCs infected ex vivo with HCV, was impaired, but this was reversed by 1‐mT treatment. This suggests that IDO inhibitors may be used to treat chronic HCV patients in vivo, in conjunction with current therapies, or to activate DCs from patients ex vivo, such that they can be administered back as a DC‐based therapeutic vaccine.     

The IL‐13/IL‐4Rα axis is involved in tuberculosis‐associated pathology

Human tuberculosis (TB) is a leading global health threat and still constitutes a major medical challenge. However, mechanisms governing tissue pathology during post‐primary TB remain elusive, partly because genetically or immunologically tractable animal models are lacking. In human TB, the demonstration of a large relative increase in interleukin (IL)‐4 and IL‐13 expression, which correlates with lung damage, indicates that a subversive T helper (TH)2 component in the response to Mycobacterium tuberculosis (Mtb) may undermine protective immunity and contribute to reactivation and tissue pathology. Up to now, there has been no clear evidence regarding whether IL‐4/IL‐13‐IL‐4 receptor‐α (Rα)‐mediated mechanisms may in fact cause reactivation and pathology. Unfortunately, the virtual absence of centrally necrotizing granulomas in experimental murine TB is associated with a poor induction of a TH2 immune response. We therefore hypothesize that, in mice, an increased production of IL‐13 may lead to a pathology similar to human post‐primary TB. In our study, aerosol Mtb infection of IL‐13‐over‐expressing mice in fact resulted in pulmonary centrally necrotizing granulomas with multinucleated giant cells, a hypoxic rim and a perinecrotic collagen capsule, with an adjacent zone of lipid‐rich, acid‐fast bacilli‐containing foamy macrophages, thus strongly resembling the pathology in human post‐primary TB. Granuloma necrosis (GN) in Mtb‐infected IL‐13‐over‐expressing mice was associated with the induction of arginase‐1‐expressing macrophages. Indirect blockade of the endogenous arginase inhibitor l ‐hydroxyarginine in Mtb‐infected wild‐type mice resulted in a strong arginase expression and precipitated a similar pathology of GN. Together, we here introduce an experimental TB model that displays many features of centrally necrotizing granulomas in human post‐primary TB and demonstrate that IL‐13/IL‐4Rα‐dependent mechanisms leading to arginase‐1 expression are involved in TB‐associated tissue pathology. © 2014 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.     

Residual LCMV antigen in transiently CD4+ T cell‐depleted mice induces high levels of virus‐specific antibodies but only limited B‐cell memory

Infection of C57BL/6 mice with lymphocytic choriomeningitis virus (LCMV) strain Armstrong (Arm) induces an acute infection with rapid virus clearance by CD8⁺ T cells independently of CD4⁺ T cell help. Residual viral antigen may, however, persist for a prolonged time. Here, we demonstrate that mice that had been transiently depleted of CD4⁺ T cells during acute LCMV Arm infection generated high levels of virus‐specific IgG antibodies (Ab) after viral clearance. Robust induction of LCMV‐specific IgG after transient CD4⁺ T cell depletion was dependent on Fcγ receptors but not on the complement receptors CD21/CD35. In contrast to the potent production of LCMV‐specific IgG, the generation of LCMV‐specific isotype‐switched memory B cells after transient CD4⁺ T cell depletion was considerably reduced. Moreover, mice depleted of CD4⁺ T cells during acute infection were strongly impaired in generating a secondary LCMV‐specific B cell response upon LCMV rechallenge. In conclusion, our data indicate that LCMV antigen depots after viral clearance were capable of inducing high levels of virus‐specific IgG. They failed, however, to induce robust virus‐specific B cell memory revealing a previously unappreciated dichotomy of specific Ab production and memory cell formation after priming with residual antigen.     

Suppression of the allogeneic response by the anti‐allergy drug N‐(3,4‐dimethoxycinnamonyl) anthranilic acid results from T‐cell cycle arrest

Previously we have shown that indoleamine 2,3‐dioxygenase (IDO) and the tryptophan metabolite, 3‐hydroxykynurenine (3HK) can prolong corneal allograft survival. IDO modulates the immune response by depletion of the essential amino acid tryptophan by breakdown to kynurenines, which themselves act directly on T lymphocytes. The tryptophan metabolite analogue N‐(3,4‐dimethoxycinnamonyl) anthranilic acid (DAA, ‘Tranilast’) shares the anthranilic acid core with 3HK. Systemic administration of DAA to mice receiving a fully MHC‐mismatched allograft of cornea or skin resulted in significant delay in rejection (median survival of controls 12 days, 13 days for cornea and skin grafts, respectively, and of treated mice 24 days (P < 0·0001) and 17 days (P < 0·03), respectively). We provide evidence that DAA‐induced suppression of the allogeneic response, in contrast to that induced by tryptophan metabolites, was a result of cell cycle arrest rather than T‐cell death. Cell cycle arrest was mediated by up‐regulation of the cell cycle‐specific inhibitors p21 and p15, and associated with a significant reduction in interleukin‐2 production, allowing us to characterize a novel mechanism for DAA‐induced T‐cell anergy. Currently licensed as an anti‐allergy drug, the oral bioavailability and safe therapeutic profile of DAA make it a candidate for the prevention of rejection of transplanted cornea and other tissues.