The diagnostic significance of PGGT1B in psoriasis.

Psoriasis is a chronic and recurrent inflammatory skin disorder driven by a complex cascade of inflammatory mediators. The present study focused on the potential clinical significance of PGGT1B in psoriasis development. The peripheral blood mononuclear cells (PBMCs) were isolated from 81 psoriasis patients and 84 healthy controls, and the expression levels of PGGT1B in PBMCs were examined by quantitative real-time polymerase chain reaction (RT-qPCR) methods. Furthermore, we tested the relationship between the level of PGGT1B in PBMCs and psoriasis severity. Also, we analyzed the potential significance of PGGT1B in psoriasis diagnosis. Finally, patients with psoriasis were divided into progressive and stable stage groups, and the differential expression of PGGT1B, TNF-α, IL-17, and IFN-γ between different phases were analyzed. PGGT1B was dramatically decreased in the psoriasis patients' PBMCs and negatively correlated with the Psoriasis Area and Severity Index (PASI). Moreover, receiver operating characteristics analysis showed the potential of differentially expressed PGGT1B in terms of distinguishing psoriasis patients from healthy controls. Finally, compared to the patients in the stable phase, PGGT1B was markedly reduced in patients' PBMCs in the progressive stage, while proinflammatory cytokines TNF-α and IL-17 were notably increased. PGGT1B was downregulated in psoriasis patients' PBMCs and may serve as a potential biomarker for the diagnosis and treatment of psoriasis.

Tumor necrosis factors-α inhibition-induced paradoxical psoriasis: A case series and literature review.

Today, anti-12/IL23, anti-IL17, and anti-IL23 provide more efficacious and/or safer treatment options for psoriasis. Though, anti-TNF remains a gold standard in the therapy of chronic inflammatory diseases. Paradoxical psoriasis has been reported to occur in patients treated with TNF-α inhibitors. According to the existing literature, including case reports, most patients with paradoxical psoriasis chose to stop the treatment immediately. This article presents a case series involving 150 patients with psoriasis who received treatments with TNF-α inhibitors. We observed 10 (6.7%) patients developing paradoxical psoriasis, and they rejected the recommendation of immediate discontinuation and decided to continue the original treatment. Surprisingly, 80% of them achieved remission again after the aggravation of symptoms and did not have any other serious adverse event. However, there is currently little research that has clarified the mechanism of paradoxical psoriasis. Therefore, we also presented a review of the literature to determine the pathogenesis of paradoxical psoriasis and speculated on the possible causes of the observed transient exacerbation cases. Investigation of the pathogenesis of this paradoxical adverse reaction not only is helpful to guide clinicians to better manage patients, but also may contribute to the discovery of new therapeutic targets in the future.

Tapering and discontinuation of systemic medications in psoriasis patients with low disease activity.

Psoriasis is a chronic disease and often requires long-term treatment, especially in patients with moderate-to-severe psoriasis. It remains controversial whether the doses of systemic medications could be tapered or if these medications could be discontinued among patients in clinical remission. In this review, we summarize whether it is possible to taper or discontinue methotrexate, cyclosporine, and biologics while controlling the relapse rates of psoriasis. Based on the current evidence, methotrexate and biologics should not be discontinued for psoriasis patients with low disease activity. However, the doses of these medications could be tapered by reducing the maintenance dose or increasing the between-dose intervals. If the disease recurs, methotrexate and biologics should be restarted at their standard doses, and for cyclosporine, the dose can be maintained or discontinued progressively. If patients relapse, cyclosporine can be given again. The decisions to taper or discontinue anti-psoriasis drugs need to account for both benefits and risks and should be individualized according to patients' disease severity, quality of life, and presence of comorbidities.

Macrophage pyroptosis induced by Candida albicans.

Candida albicans (C. albicans) is a prevalent opportunistic pathogen that causes mucocutaneous and systemic infections, particularly in immunocompromised individuals. Macrophages play a crucial role in eliminating C. albicans in local and bloodstream contexts, while also regulating antifungal immune responses. However, C. albicans can induce macrophage lysis through pyroptosis, a type of regulated cell death. This process can enable C. albicans to escape from immune cells and trigger the release of IL-1ß and IL-18, which can impact both the host and the pathogen. Nevertheless, the mechanisms by which C. albicans triggers pyroptosis in macrophages and the key factors involved in this process remain unclear. In this review, we will explore various factors that may influence or trigger pyroptosis in macrophages induced by C. albicans, such as hypha, ergosterol, cell wall remodeling, and other virulence factors. We will also examine the possible immune response following macrophage pyroptosis.

Ferrostatin-1 alleviates skin inflammation and inhibits ferroptosis of neutrophils and CD8+ T cells in allergic contact dermatitis.

BACKGROUND: Ferroptosis is considered as an immunogenic type of regulated cell death and associated with the pathogenesis of inflammatory skin diseases. However, the involvement and function of ferroptosis in allergic contact dermatitis (ACD) remains unknown. OBJECTIVE: To explore the role of ferroptosis in ACD. To reveal which type of cells develops ferroptosis in ACD. METHODS: We detected the key markers of ferroptosis in 1-Chloro-2,4-dinitrochlorobenzene (DNCB)-induced ACD mice model. We applicated ferrostatin-1 (Fer-1) to restrain ferroptosis in ACD mice and then compared the severity of dermatitis and the level of inflammation and ferroptosis in dermis and epidermis, respectively. Keratinocyte-specific Gpx4 conditional knockout (cKO) mice were used to investigate the function of keratinocyte ferroptosis in the development of ACD. Single-cell RNA sequencing was conducted to analyze the affection of Fer-1 on different type of cells in ACD. RESULTS: Ferroptosis was involved in DNCB-induced ACD mice. Ferroptosis activation was more remarkable in dermis rather than in epidermis. Gpx4 cKO mice showed similar severity of skin dermatitis as control mice. Fer-1 alleviated skin inflammation in mice and reduced ferroptosis in neutrophils and CD8+ T cells both of which contribute to development of ACD. CONCLUSION: Ferroptosis was activated in immune cells, especially neutrophils and CD8+ T cells in DNCB-induced ACD mice. Fer-1 treatment inhibited ferroptosis of neutrophils and CD8+ T cells and relieved skin damage in ACD mice.

Gasdermin E promotes translocation of p65 and c-jun into nucleus in keratinocytes for progression of psoriatic skin inflammation.

Gasdermin E (GSDME) has recently been identified as a critical executioner to mediate pyroptosis. While epidermal keratinocytes can initiate GSDME-mediated pyroptosis, the role of keratinocyte GSDME in psoriatic dermatitis remains poorly characterized. Through analysis of GEO datasets, we found elevated GSDME levels in psoriatic lesional skin. Additionally, GSDME levels correlated with both psoriasis severity and response to biologics treatments. Single-cell RNA sequencing (scRNA-seq) from a GEO dataset revealed GSDME upregulation in keratinocytes of psoriasis patients. In the imiquimod (IMQ)-induced psoriasis-like dermatitis mouse model, both full-length and cleaved forms of caspase-3 and GSDME were elevated in the epidermis. Abnormal proliferation and differentiation of keratinocytes and dermatitis were attenuated in Gsdme-/- mice and keratinocyte-specific Gsdme conditional knockout mice after IMQ stimulation. Exposure of keratinocytes to mixed cytokines (M5), mimicking psoriatic conditions, led to GSDME cleavage. Moreover, the interaction between GSDME-FL and p65 or c-jun was significantly increased after M5 stimulation. GSDME knockdown inhibited nuclear translocation of p65 and c-jun and decreased upregulation of psoriatic inflammatory mediators such as IL1ß, CCL20, CXCL1, CXCL8, S100A8, and S100A9 in M5-challenged keratinocytes. In conclusion, GSDME in keratinocytes contributes to the pathogenesis and progression of psoriasis, potentially in a pyroptosis-independent manner by interacting and promoting translocation of p65 and c-jun. These findings suggest that keratinocyte GSDME could serve as a potential therapeutic target for psoriasis treatment.

Association between the neutrophil-to-lymphocyte ratio and psoriasis: a cross-sectional study of the National Health and Nutrition Examination Survey 2011-2014.

OBJECTIVES: To investigate the association between the neutrophil-to-lymphocyte ratio (NLR) and psoriasis. DESIGN: Cross-sectional study. SETTING: National Health and Nutrition Examination Survey 2011-2014. PARTICIPANTS: A subsample of 8387 individuals aged 18 years and older were screened for inclusion, of whom 238 reported a diagnosis of psoriasis. PRIMARY AND SECONDARY OUTCOME MEASURES: Psoriasis and the severity of psoriasis were defined according to participants' self-reports. Weighted logistic regression, subgroup and restricted cubic spline (RCS) analyses were conducted to estimate the potential relationship of the NLR with psoriasis. RESULTS: In the fully adjusted models, the fourth quartile of the NLR was significantly and positively associated with the presence of psoriasis using the first quartile as a reference (OR: 2.22, 95% CI: 1.27 to 3.87, p=0.01). Elevated NLR was associated with an increased odds of having more severe psoriasis for the highest quartile (vs the lowest quartile), with an OR of 2.43 (95% CI: 1.10 to 5.36, p=0.003). The association between the NLR and psoriasis differed across prespecified subgroups by age, sex, race, income and education. A non-linear correlation of the NLR with psoriasis was observed using univariable and multivariable RCS (all p for non-linearity <0.05). CONCLUSIONS: The NLR was non-linearly and positively correlated with the presence of psoriasis, and our findings suggest a significant association between the NLR and the severity of psoriasis. The potential role and value in the clinical diagnosis and prognostic assessment of the NLR in psoriasis calls for further longitudinal studies.

Gasdermin D-mediated keratinocyte pyroptosis as a key step in psoriasis pathogenesis.

Gasdermin D (GSDMD)-mediated pyroptosis has a significant pro-inflammation characteristic due to dramatic secretion of pro-inflammatory substances. However, its role remains unclear in psoriasis as one chronic inflammatory skin disorder with high prevalence. We found that N-terminal GSDMD (N-GSDMD) was aberrantly expressed in epidermis of skin lesion in psoriasis patients and imiquimod-induced psoriasis-like dermatitis (IIPLD) mice. In epidermis of IIPLD mice and M5 (simulating psoriatic inflammatory challenge)-treated keratinocytes cultured in vitro, cleavage products of caspase-1, GSDMD and IL-1ß were increased. M5-stimulated keratinocyte presented typical pyroptosis morphology accompanied with PI-staining. Gsdmd-/- keratinocytes could not present pyroptosis morphology while stimulated with M5. Electroporation of recombinant N-GSDMD could make the pyroptosis morphology reappear. In Gsdmd-/- mice or keratinocyte-specific Gsdmd conditional knockout mice, we observed the alleviation of psoriatic inflammation and epidermal aberrant expression of Ki-67 and differentiation markers (loricrin and keratin 5) after imiquimod stimulation. Transplanting skin tissue from control mice to Gsdmd-/- mice can evoke the response to imiquimod stimulation in the background of Gsdmd-/- mice (not limited in transplanting area). In M5-stimulated keratinocytes, disulfiram or GSDMD siRNA transfection can inhibit pyroptosis and eliminate disproportionate increases of Ki-67 and PI. We further validated that topically application of disulfiram (pyroptosis inhibitor) also alleviated IIPLD in mice. These findings indicate a novel mechanism that GSDMD-mediated keratinocyte pyroptosis facilitates hyperproliferation and aberrant differentiation induced by immune microenvironment in psoriatic skin inflammation, which contributes to pathogenesis of psoriasis. Our study provides an innovative insight that targeting pyroptosis can be considered as a therapeutic strategy against psoriasis.

Reduction of miR-133a-3p contributes to apoptosis and gasdermin E-mediated pyroptosis of keratinocytes in skin exposed to ultraviolet B radiation.

Engagement of regulated cell death in keratinocytes plays a crucial role in the pathogenesis and development of skin disorders associated with UV radiation. However, it remains unclear how microRNAs (miRNAs) participate in the regulation of UV-caused keratinocyte death. In this study, we found that miR-133a-3p was decreased in the epidermis of UVB-challenged mice and UVB-irradiated keratinocyte cell line HaCaT cells. The intradermal injection of agomir miR-133a-3p ameliorated skin damage of UVB-challenged mice, especially epidermal necrosis. Meanwhile, the injection inhibited apoptosis indicator PARP cleavage and pyroptosis indicator GSDME cleavage in the epidermis. In UVB-challenged HaCaT cells, transfection of miR-133a-3p mimic or inhibitor alleviated or aggravated UVB-induced apoptosis and GSDME-mediated pyroptosis respectively. miR-133a-3p was also involved in the effects of metformin treatment on alleviating skin damage in UVB-challenged mice and on inhibiting apoptosis and GSDME-mediated pyroptosis in UVB-irradiated HaCaT cells. We confirmed that CYLD is a target gene of miR-133a-3p and participates in the protective effects of miR-133a-3p on inhibiting UVB-caused apoptosis and GSDME-mediated pyroptosis in keratinocytes. This study indicates a pivotal role for miR-133a-3p of keratinocytes in UVB-caused skin damage. Alleviating skin photodamage by restoring the decrease of miR-133a-3p can be considered a potential therapeutic approach.

The HDAC inhibitor zabadinostat is a systemic regulator of adaptive immunity.

Protein acetylation plays a key role in regulating cellular processes and is subject to aberrant control in diverse pathologies. Although histone deacetylase (HDAC) inhibitors are approved drugs for certain cancers, it is not known whether they can be deployed in other therapeutic contexts. We have explored the clinical HDAC inhibitor, zabadinostat/CXD101, and found that it is a stand-alone regulator of the adaptive immune response. Zabadinostat treatment increased expression of MHC class I and II genes in a variety of cells, including dendritic cells (DCs) and healthy tissue. Remarkably, zabadinostat enhanced the activity of DCs, and CD4 and CD8 T lymphocytes. Using an antigenic peptide presented to the immune system by MHC class I, zabadinostat caused an increase in antigen-specific CD8 T lymphocytes. Further, mice immunised with covid19 spike protein and treated with zabadinostat exhibit enhanced covid19 neutralising antibodies and an increased level of T lymphocytes. The enhanced humoral response reflected increased activity of T follicular helper (Tfh) cells and germinal centre (GC) B cells. Our results argue strongly that zabadinostat has potential to augment diverse therapeutic agents that act through the immune system.

Long non-coding RNA-derived peptides are immunogenic and drive a potent anti-tumour response.

Protein arginine methyltransferase (PRMT) 5 is over-expressed in a variety of cancers and the master transcription regulator E2F1 is an important methylation target. We have explored the role of PRMT5 and E2F1 in regulating the non-coding genome and report here a striking effect on long non-coding (lnc) RNA gene expression. Moreover, many MHC class I protein-associated peptides were derived from small open reading frames in the lncRNA genes. Pharmacological inhibition of PRMT5 or adjusting E2F1 levels qualitatively altered the repertoire of lncRNA-derived peptide antigens displayed by tumour cells. When presented to the immune system as either ex vivo-loaded dendritic cells or expressed from a viral vector, lncRNA-derived peptides drove a potent antigen-specific CD8 T lymphocyte response, which translated into a significant delay in tumour growth. Thus, lncRNA genes encode immunogenic peptides that can be deployed as a cancer vaccine.

The emerging role of neutrophil extracellular traps in fungal infection.

Fungal infections are global public health problems and can lead to substantial human morbidity and mortality. Current antifungal therapy is not satisfactory, especially for invasive, life-threatening fungal infections. Modulating the antifungal capacity of the host immune system is a feasible way to combat fungal infections. Neutrophils are key components of the innate immune system that resist fungal pathogens by releasing reticular extracellular structures called neutrophil extracellular traps (NETs). When compared with phagocytosis and oxidative burst, NETs show better capability in terms of trapping large pathogens, such as fungi. This review will summarize interactions between fungal pathogens and NETs. Molecular mechanisms of fungi-induced NETs formation and defensive strategies used by fungi are also discussed.

Ferroptosis: Mechanism and connections with cutaneous diseases.

Ferroptosis is a recognized novel form of programmed cell death pathway, featuring abnormalities in iron metabolism, SystemXc-/glutathione axis, and lipid peroxidation regulation. A variety of ferroptosis inducers can influence glutathione peroxidase directly or indirectly via diverse pathways, leading to decreased antioxidant capacity, accumulated cellular lipid peroxides, and finally inducing ferroptosis. To date, mounting studies confirm the association of ferroptosis with various cutaneous diseases, including skin homeostasis, neoplastic diseases, infectious diseases, genetic skin disease, inflammatory skin diseases, and autoimmune diseases. There are shared characteristics regarding ferroptosis and various cutaneous diseases in terms of pathophysiological mechanisms, such as oxidative stress associated with iron metabolism disorder and accumulated lipid peroxides. Therefore, we summarize the current knowledge regarding the mechanisms involved in the regulation of ferroptosis for further discussion of its role in the pathogenesis and prognosis of skin diseases. Gaining insight into the underlying mechanisms of ferroptosis and the associated dermatological disorders could illuminate the pathogenesis and treatments of different cutaneous diseases.

GSDME deficiency leads to the aggravation of UVB-induced skin inflammation through enhancing recruitment and activation of neutrophils.

Gasdermin E (GSDME)-mediated pyroptosis is induced in keratinocytes of UVB-challenged skin. The role of GSDME in UVB-caused skin damage remains unknown. To explore the role of GSDME in UVB-induced skin inflammation. We compared differences in skin appearance, histological features, keratinocyte death modalities, infiltration of immune cells, and levels of some inflammatory cytokines between Gsdme-/- mice and wild type (WT) mice after UVB exposure. We explored whether keratinocytes contribute to GSDME deficiency-caused aggravation of UVB-induced skin inflammation in GSDME knockdown keratinocyte cultured in vitro and keratinocyte-specific Gsdme conditional knockout mice. We used anti-Ly6G antibody to deplete neutrophils and explore their role in UVB-caused skin damage. Skin damage and neutrophils infiltration were aggravated in UVB-challenged Gsdme-/- mice, compared with UVB-challenged WT mice. Apoptosis and necroptosis, which were initiated together with GSDME-mediated pyroptosis in UVB-challenged WT mice, were not enhanced in UVB-challenged Gsdme-/- mice. Neutrophils activation indicators and its recruiting cytokines were increased in skin tissue of UVB-challenged Gsdme-/- mice. However, GSDME knockdown did not lead to the further increase of mRNA and secretion of TNF-α and IL-6 in UVB-challenged keratinocytes. Skin damage was not aggravated in UVB-challenged Gsdme cKO mice. Neutrophils depletion alleviated UVB-caused skin damage in WT mice and Gsdme-/- mice, and eliminated its aggravation in Gsdme-/- mice. This study demonstrates that GSDME plays a restrictive role in UVB-induced skin damage through inhibiting excessive recruitment and activation of neutrophils in the immune microenvironment in UVB-caused skin inflammation. However, keratinocytes might not contribute to this restrictive function.

Necroptosis-mediated HMGB1 secretion of keratinocytes as a key step for inflammation development in contact hypersensitivity.

Keratinocyte necroptosis (with proinflammatory characteristic) is required for epidermal damage in contact hypersensitivity (CHS). In DNCB-induced CHS mice model, we observed the aggravated keratinocyte death and increased phosphorylation level of MLKL, RIPK3 and RIPK1. However, CHS skin lesion did not present in keratinocyte-specific Mlkl knockout mice. We validated that MLKL-mediated keratinocyte necroptosis is required for epidermal damage in response to immune microenvironment in CHS. Moreover, MLKL-mediated necroptosis deficiency or inhibition resulted in blocking recruitment and activation of inflammatory cells in CHS via reducing HMGB1 release in keratinocytes. This study suggests that MLKL-mediated keratinocyte necroptosis functions as a self-amplified actor in inflammatory responses and could be considered as an effective therapeutic target. It proposes an innovative prospective that inhibiting keratinocyte necroptosis can prevent the development of epidermal damage in CHS.

Fatal COVID-19 outcomes are associated with an antibody response targeting epitopes shared with endemic coronaviruses.

The role of immune responses to previously seen endemic coronavirus epitopes in severe acute respiratory coronavirus 2 (SARS-CoV-2) infection and disease progression has not yet been determined. Here, we show that a key characteristic of fatal outcomes with coronavirus disease 2019 (COVID-19) is that the immune response to the SARS-CoV-2 spike protein is enriched for antibodies directed against epitopes shared with endemic beta-coronaviruses and has a lower proportion of antibodies targeting the more protective variable regions of the spike. The magnitude of antibody responses to the SARS-CoV-2 full-length spike protein, its domains and subunits, and the SARS-CoV-2 nucleocapsid also correlated strongly with responses to the endemic beta-coronavirus spike proteins in individuals admitted to an intensive care unit (ICU) with fatal COVID-19 outcomes, but not in individuals with nonfatal outcomes. This correlation was found to be due to the antibody response directed at the S2 subunit of the SARS-CoV-2 spike protein, which has the highest degree of conservation between the beta-coronavirus spike proteins. Intriguingly, antibody responses to the less cross-reactive SARS-CoV-2 nucleocapsid were not significantly different in individuals who were admitted to an ICU with fatal and nonfatal outcomes, suggesting an antibody profile in individuals with fatal outcomes consistent with an "original antigenic sin" type response.

CXCR6 is a marker for protective antigen-specific cells in the lungs after intranasal immunization against Mycobacterium tuberculosis.

Convincing correlates of protective immunity against tuberculosis have been elusive. In BALB/c mice, intranasal immunization with a replication-deficient recombinant adenovirus expressing Mycobacterium tuberculosis antigen 85A (adenovirus-85A) induces protective lower respiratory tract immunity against pulmonary challenge with Mycobacterium tuberculosis, while intradermal immunization with adenovirus-85A does not. Here we report that intranasal immunization with adenovirus-85A induces expression of the chemokine receptor CXCR6 on lung CD8 T lymphocytes, which is maintained for at least 3 months. CXCR6-positive antigen-specific T cell numbers are increased among bronchoalveolar lavage-recoverable cells. Similarly, intranasal immunization with recombinant antigen 85A with adjuvant induces CXCR6 expression on lung CD4 cells in BALB/c and C57BL/6 mice, while a synthetic ESAT6(1-20) peptide with adjuvant induces CXCR6 expression in C57BL/6 mice. Parenteral immunization fails to do so. Upregulation of CXCR6 is accompanied by a transient elevation of serum CXCL16 after intranasal immunization, and lung cells cultured ex vivo from mice immunized intranasally show increased production of CXCL16. Administration of CXCL16 and cognate antigen intranasally to mice previously immunized parenterally increases the number of antigen-specific T lymphocytes in the bronchoalveolar lavage-recoverable population, which mediates inhibition of the early growth of Mycobacterium tuberculosis after challenge. We conclude that expression of CXCR6 on lung T lymphocytes is a correlate of local protective immunity against Mycobacterium tuberculosis after intranasal immunization and that CXCR6 and CXCL16 play an important role in the localization of T cells within lung tissue and the bronchoalveolar lavage-recoverable compartment.

CD4 T-cell help programs a change in CD8 T-cell function enabling effective long-term control of murine gammaherpesvirus 68: role of PD-1-PD-L1 interactions.

We previously showed that agonistic antibodies to CD40 could substitute for CD4 T-cell help and prevent reactivation of murine gammaherpesvirus 68 (MHV-68) in the lungs of major histocompatibility complex (MHC) class II(-/-) (CII(-/-)) mice, which are CD4 T cell deficient. Although CD8 T cells were required for this effect, no change in their activity was detected in vitro. A key question was whether anti-CD40 treatment (or CD4 T-cell help) changed the function of CD8 T cells or another cell type in vivo. To address this question, in the present study, we showed that adoptive transfer of CD8 T cells from virus-infected wild-type mice or anti-CD40-treated CII(-/-) mice caused a significant reduction in lung viral titers, in contrast to those from control CII(-/-) mice. Anti-CD40 treatment also greatly prolonged survival of infected CII(-/-) mice. This confirms that costimulatory signals cause a change in CD8 T cells enabling them to maintain effective long-term control of MHV-68. We investigated the nature of this change and found that expression of the inhibitory receptor PD-1 was significantly increased on CD8 T cells in the lungs of MHV-68-infected CII(-/-), CD40(-/-), or CD80/86(-/-) mice, compared with that in wild-type or CD28/CTLA4(-/-) mice, correlating with the level of viral reactivation. Furthermore, blocking PD-1-PD-L1 interactions significantly reduced viral reactivation in CD4 T-cell-deficient mice. In contrast, the absence of another inhibitory receptor, NKG2A, had no effect. These data suggest that CD4 T-cell help programs a change in CD8 T-cell function mediated by altered PD-1 expression, which enables effective long-term control of MHV-68.

A mouse model of lethal synergism between influenza virus and Haemophilus influenzae.

Secondary bacterial infections that follow infection with influenza virus result in considerable morbidity and mortality in young children, the elderly, and immunocompromised individuals and may also significantly increase mortality in normal healthy adults during influenza pandemics. We herein describe a mouse model for investigating the interaction between influenza virus and the bacterium Haemophilus influenzae. Sequential infection with sublethal doses of influenza and H. influenzae resulted in synergy between the two pathogens and caused mortality in immunocompetent adult wild-type mice. Lethality was dependent on the interval between administration of the bacteria and virus, and bacterial growth was prolonged in the lungs of dual-infected mice, although influenza virus titers were unaffected. Dual infection induced severe damage to the airway epithelium and confluent pneumonia, similar to that observed in victims of the 1918 global influenza pandemic. Increased bronchial epithelial cell death was observed as early as 1 day after bacterial inoculation in the dual-infected mice. Studies using knockout mice indicated that lethality occurs via a mechanism that is not dependent on Fas, CCR2, CXCR3, interleukin-6, tumor necrosis factor, or Toll-like receptor-4 and does not require T or B cells. This model suggests that infection with virulent strains of influenza may predispose even immunocompetent individuals to severe illness on secondary infection with H. influenzae by a mechanism that involves innate immunity, but does not require tumor necrosis factor, interleukin-6, or signaling via Toll-like receptor-4.

Multiple mechanisms contribute to impairment of type 1 interferon production during chronic lymphocytic choriomeningitis virus infection of mice.

Type 1 IFNs, innate cytokines with important effector and immunomodulatory properties, are rapidly induced in the acute phase of many virus infections; however, this is generally a transient response that is not sustained during virus persistence. To gain insight into mechanisms that can contribute to down-regulation of type 1 IFN production during virus persistence, we analyzed type 1 IFN production during acute and chronic lymphocytic choriomeningitis virus (LCMV) infection. High-level type 1 IFN production was transiently up-regulated in cells including plasmacytoid and conventional dendritic cells (DCs) following LCMV infection of mice, but LCMV persistence was associated with only low-level type 1 IFN production. Nonetheless, chronically infected mice were able to up-regulate type 1 IFN production in response to TLR3, 7, and 9 ligands, albeit less efficiently than uninfected mice. Splenic DC numbers in mice chronically infected with LCMV were decreased, and the remaining cells exhibited a reduced response to TLR stimulation. LCMV-infected cell lines efficiently up-regulated type 1 IFN production following TLR ligation and infection with a DNA virus, but exhibited a defect in type 1 IFN induction following infection with Sendai, an RNA virus. This block in type 1 IFN production by infected cells, together with abnormalities in DC numbers and functions, likely contribute to the low-level type 1 IFN production in mice chronically infected with LCMV. Impairment of type 1 IFN production may both promote virus persistence and impact on host immunocompetence. Understanding the mechanisms involved may assist in development of strategies for control of virus persistence and superinfection.