Immune-mediated Lung Injury Research Articles

IFN-γ Limits Immunopathogenesis but Delays Fungal Clearance during Pneumocystis Pneumonia.

High levels of IFN-γ are produced in the lung during an adaptive immune response to Pneumocystis, but the effects of this prototypical Th1 cytokine on fungal clearance and immunopathogenesis have not been fully defined. Therefore, Pneumocystis-infected immunodeficient mice were immune reconstituted and administered control or anti-IFN-γ neutralizing Ab to determine how IFN-γ regulates the balance between host defense and immune-mediated lung injury. Mice treated with anti-IFN-γ demonstrated an initial worsening of Pneumocystis pneumonia-related immunopathogenesis, with greater weight loss, heightened lung inflammation, and more severe pulmonary function deficits than control mice. However, IFN-γ neutralization also enhanced macrophage phagocytosis of Pneumocystis and accelerated fungal clearance. When anti-IFN-γ-treated mice were also given IL-4 and IL-13 to promote a Th2-biased lung environment, the accelerated fungal clearance was preserved, but the severity of immunopathogenesis was reduced, and a more rapid recovery was observed. A direct suppressive effect of IFN-γ on macrophages was required but was not solely responsible for delayed fungal clearance, suggesting that IFN-γ acts through multiple mechanisms that likely include modulation of both macrophage and Th polarization. Enhanced Pneumocystis clearance in anti-IFN-γ-treated and IFN-γR-deficient mice was associated with significantly elevated IL-17+ CD4+ T cells and IL-17 protein in the lungs. Furthermore, neutralization of IL-17, but not IL-4, signaling blocked the accelerated fungal clearance observed in anti-IFN-γ-treated mice. Together, these data demonstrate that although IFN-γ delays fungal clearance by suppressing the lung Th17 response, it also serves an important regulatory role that limits immunopathogenesis and preserves pulmonary function.

Lung injury induces a polarized immune response by self-antigen-specific CD4+ Foxp3+ regulatory T cells

Self-antigen-specific Tcells are prevalent in the mature adaptive immune system but are regulated through multiple mechanisms of tolerance. However, inflammatory conditions such as tissue injury may allow these Tcells to break tolerance and trigger autoimmunity. To understand how the Tcell repertoire responds to the presentation of self-antigen under highly stimulatory conditions, we use peptide:major histocompatibility complex (MHC) class II tetramers to track the behavior of endogenous CD4+ Tcells with specificity to a lung-expressed self-antigen in mouse models of immune-mediated lung injury. Acute injury results in the exclusive expansion of CD4+ regulatory Tcells (Tregs) that is dependent on self-antigen recognition andinterleukin-2 (IL-2). Conversely, conventional CD4+ Tcells of the same self-antigen specificity remain unresponsive even following Treg ablation. Thus, the self-antigen-specific CD4+ Tcell repertoire is poised to serve a regulatory function during acute tissue damage to limit further damage and the possibility of autoimmunity.

Lactate Dehydrogenase can be Considered a Predictive Marker of Severity and Mortality of Covid-19 in Diabetic and Non-Diabetic Patients. A Case Series

Case Series PresentationEight elderly confirmed SARS-CoV-2 patients who had severe course of COVID-19 and admitted to ICU expressed high lactate dehydrogenase (LDH) above normal level. The mean value of LDH was 440.40 U/L with 84.52 standard deviation (normal range = 100 – 190 U/L). The mean age of patients was 73.63 years (standard deviation = 3.34). The patients were 4 males (50%) and 4 females (50%). The median of stay duration at ICU was 2 days (range = 1-32 days). Four patients died (50%) and four patients survived (50%). All the patients were at the same ICU and received the same treatment course for COVID-19. DiscussionIt has been shown that LDH is a potential marker of vascular permeability in immune-mediated lung injury. Areas within the body where LDH are most active include the liver, striated muscles, heart, kidneys, lungs, brain, and red blood cells. LDH is a known marker for different inflammatory states, sepsis, myocardial infarctions, infections, and malignancies. One study showed that LDH elevation was associated with a 6-fold increase in the odds of developing a severe COVID-19 disease. Furthermore elevated LDH was associated with a 16 fold increase in patient mortality. Elevated LDH levels seem to reflect that the multiple organ injury and failure may play a more prominent role in influencing the clinical outcomes in patients with COVID-19. This study is a report of 8 elderly critically ill COVID-19 patients who expressed high lactate dehydrogenase above normal level. This indicates that lactate dehydrogenase can predict the outcome of elderly COVID-19 patients. All the eight patients developed severe course of COVID-19, four of them died. ConclusionHigh levels of lactate dehydrogenase can predict the severity and mortality of COVID-19 in elderly patients. LDH levels could be considered for inclusion in future risk stratification models for COVID-19 severity and mortality. More observational studies

Pleuroparenchymal Fibroelastosis in Chronic Graft-versus-Host-Disease

<h3>Purpose</h3> Pleuroparenchymal fibroelastosis (PPFE) is a rare entity of interstitial lung disease previously reported in both lung and hematopoietic stem cell transplant (HCT) recipients. The association between PPFE and chronic Graft-versus-Host Disease (cGVHD) has not been established. <h3>Methods</h3> Patients on cGVHD protocols (NCT00092235; NCT02669251) between 10/01/2004 and 01/31/2020 were included. An independent committee of two transplant hematologists, one cardiothoracic radiologist, and three transplant pulmonologists reviewed patients' demographic and HCT information, pulmonary function tests (PFT), and thoracic CT scans. The diagnosis of PPFE was adapted from the 2013 ATS/ERS Interstitial Lung Disease Consensus Statement (Table 1). <h3>Results</h3> PPFE was diagnosed in 0.8% (3/374) of patients (Table 2). All were female with body mass index (BMI) <18.5kg/m². Patients 2 and 3 had classical Hodgkin lymphoma (cHL) with intrathoracic involvement, received bleomycin (patient 2 and 3) and mediastinal radiation (patient 2) prior to HCT. All had severe cGVHD, requiring 1-5 lines of systemic immunosuppressive therapy. Before the development of PPFE, Patients 2 and 3 had viral pneumonia, while patient 1 had no documented pulmonary infection. Lung biopsies in all patients showed non-specific inflammation and fibrosis; of note, all were performed before the definition of PPFE as a clinical entity in 2013, and did not include the pleura or subpleural parenchyma. At data cut-off (April 2021), all patients were alive. Median time from HCT to PPFE diagnosis was 5.5 years (range, 2-6.5), and median survival post-PPFE diagnosis was 7.5 years (range, 5.5-12). <h3>Conclusion</h3> PPFE is a rare, delayed complication of HCT which can be seen with concurrent cGVHD. The pathogenesis of PPFE is unclear but may be associated with the immune-mediated lung injury in cGVHD, infection, preexisting malignancy and lung-toxic treatment. Heightened clinical awareness for PPFE among the cGVHD population warrants further study.

Whole-genome sequencing reveals host factors underlying critical COVID-19

Critical COVID-19 is caused by immune-mediated inflammatory lung injury. Host genetic variation influences the development of illness requiring critical care1 or hospitalization2–4 after infection with SARS-CoV-2. The GenOMICC (Genetics of Mortality in Critical Care) study enables the comparison of genomes from individuals who are critically ill with those of population controls to find underlying disease mechanisms. Here we use whole-genome sequencing in 7,491 critically ill individuals compared with 48,400 controls to discover and replicate 23 independent variants that significantly predispose to critical COVID-19. We identify 16 new independent associations, including variants within genes that are involved in interferon signalling (IL10RB and PLSCR1), leucocyte differentiation (BCL11A) and blood-type antigen secretor status (FUT2). Using transcriptome-wide association and colocalization to infer the effect of gene expression on disease severity, we find evidence that implicates multiple genes—including reduced expression of a membrane flippase (ATP11A), and increased expression of a mucin (MUC1)—in critical disease. Mendelian randomization provides evidence in support of causal roles for myeloid cell adhesion molecules (SELE, ICAM5 and CD209) and the coagulation factor F8, all of which are potentially druggable targets. Our results are broadly consistent with a multi-component model of COVID-19 pathophysiology, in which at least two distinct mechanisms can predispose to life-threatening disease: failure to control viral replication; or an enhanced tendency towards pulmonary inflammation and intravascular coagulation. We show that comparison between cases of critical illness and population controls is highly efficient for the detection of therapeutically relevant mechanisms of disease.

A functionally distinct neutrophil landscape in severe COVID-19 reveals opportunities for adjunctive therapies

Acute respiratory distress syndrome (ARDS) is a life-threatening syndrome, constituted by respiratory failure and diffuse alveolar damage that results from dysregulated local and systemic immune activation, causing pulmonary vascular, parenchymal, and alveolar damage. SARS-CoV-2 infection has become the dominant cause of ARDS worldwide, and emerging evidence implicates neutrophils and their cytotoxic arsenal of effector functions as central drivers of immune-mediated lung injury in COVID-19 ARDS. However, key outstanding questions are whether COVID-19 drives a unique program of neutrophil activation or effector functions that contribute to the severe pathogenesis of this pandemic illness and whether this unique neutrophil response can be targeted to attenuate disease. Using a combination of high-dimensional single-cell analysis and ex vivo functional assays of neutrophils from patients with COVID-19 ARDS, compared with those with non-COVID ARDS (caused by bacterial pneumonia), we identified a functionally distinct landscape of neutrophil activation in COVID-19 ARDS that was intrinsically programmed during SARS-CoV-2 infection. Furthermore, neutrophils in COVID-19 ARDS were functionally primed to produce high amounts of neutrophil extracellular traps. Surprisingly, this unique pathological program of neutrophil priming escaped conventional therapy with dexamethasone, thereby revealing a promising target for adjunctive immunotherapy in severe COVID-19.

Delayed hypersensitivity to the Comirnaty coronavirus disease 2019 vaccine presenting with pneumonitis and rash

Delayed hypersensitivity to the Comirnaty coronavirus disease 2019 vaccine presenting with pneumonitis and rash

Thymosin Alpha 1 Mitigates Cytokine Storm in Blood Cells From Coronavirus Disease 2019 Patients.

BackgroundCoronavirus disease 2019 (COVID-19) is characterized by immune-mediated lung injury and complex alterations of the immune system, such as lymphopenia and cytokine storm, that have been associated with adverse outcomes underlining a fundamental role of host response in severe acute respiratory syndrome coronavirus 2 infection and the pathogenesis of the disease. Thymosin alpha 1 (Tα1) is one of the molecules used in the management of COVID-19, because it is known to restore the homeostasis of the immune system during infections and cancer. MethodsIn this study, we captured the interconnected biological processes regulated by Tα1 in CD8+ T cells under inflammatory conditions. ResultsGenes associated with cytokine signaling and production were upregulated in blood cells from patients with COVID-19, and the ex vivo treatment with Tα1-mitigated cytokine expression, and inhibited lymphocyte activation in a CD8+ T-cell subset specifically. ConclusionThese data suggest the potential role of Tα1 in modulating the immune response homeostasis and the cytokine storm in vivo.

The four horsemen of a viral Apocalypse: The pathogenesis of SARS-CoV-2 infection (COVID-19).

SummaryThe pathogenesis of coronavirus disease 2019 (COVID-19) may be envisaged as the dynamic interaction between four vicious feedback loops chained or happening at once. These are the viral loop, the hyperinflammatory loop, the non-canonical renin-angiotensin system (RAS) axis loop, and the hypercoagulation loop. Severe acute respiratory syndrome (SARS)-coronavirus (CoV)-2 lights the wick by infecting alveolar epithelial cells (AECs) and downregulating the angiotensin converting enzyme-2 (ACE2)/angiotensin (Ang-1–7)/Mas1R axis. The viral feedback loop includes evading the host's innate response, uncontrolled viral replication, and turning on a hyperactive adaptative immune response. The inflammatory loop is composed of the exuberant inflammatory response feeding back until exploding in an actual cytokine storm. Downregulation of the ACE2/Ang-(1–7)/Mas1R axis leaves the lung without a critical defense mechanism and turns the scale to the inflammatory side of the RAS. The coagulation loop is a hypercoagulable state caused by the interplay between inflammation and coagulation in an endless feedback loop. The result is a hyperinflammatory and hypercoagulable state producing acute immune-mediated lung injury and eventually, adult respiratory distress syndrome.

Immunopathogenesis of COVID-19 and early immunomodulators.

The novel coronavirus disease 2019 (COVID-19) is spreading globally. Although its etiologic agent is discovered as severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), there are many unsolved issues in COVID-19 and other infectious diseases. The causes of different clinical phenotypes and incubation periods among individuals, species specificity, and cytokine storm with lymphopenia as well as the mechanism of damage to organ cells are unknown. It has been suggested that in viral pneumonia, virus itself is not a direct cause of acute lung injury; rather, aberrant immune reactions of the host to the insults from viral infection are responsible. According to its epidemiological and clinical characteristics, SARS-CoV-2 may be a virus with low virulence in nature that has adapted to the human species. Current immunological concepts have limited ability to explain such unsolved issues, and a presumed immunopathogenesis of COVID-19 is presented under the protein-homeostasis-system hypothesis. Every disease, including COVID-19, has etiological substances controlled by the host immune system according to size and biochemical properties. Patients with severe pneumonia caused by SARS-CoV-2 show more severe hypercytokinemia with corresponding lymphocytopenia than patients with mild pneumonia; thus, early immunomodulator treatment, including corticosteroids, has been considered. However, current guidelines recommend their use only for patients with advanced pneumonia or acute respiratory distress syndrome. Since the immunopathogenesis of pneumonia may be the same for all patients regardless of age or severity and the critical immune-mediated lung injury may begin in the early stage of the disease, early immunomodulator treatment, including corticosteroids and intravenous immunoglobulin, can help reduce morbidity and possibly mortality rates of older patients with underlying conditions.

The immunology of COVID-19: is immune modulation an option for treatment?

SummaryIn December, 2019, an outbreak of COVID-19 emerged in Wuhan, China and quickly spread globally. As of May 7, 2020, there were 3 672 238 confirmed infections and 254 045 deaths attributed to COVID-19. Evidence has shown that there are asymptomatic carriers of COVID-19 who can transmit the disease to others. The virus incubation time shows a wide range (0–24 days) and the virus displays a high infectivity. It is therefore urgent to develop an effective therapy to treat patients with COVID-19 and to control the spread of the causative agent, severe respiratory syndrome coronavirus 2. Repurposing of approved drugs is widely adopted to fight newly emerged diseases such as COVID-19, as these drugs have known pharmacokinetic and safety profiles. As pathological examination has confirmed the involvement of immune hyperactivation and acute respiratory distress syndrome in fatal cases of COVID-19, several disease-modifying anti-rheumatic drugs (DMARDS), such as hydroxychloroquine and tocilizumab, have been proposed as potential therapies for the treatment of COVID-19. In this Review, we discuss the immunological aspects of COVID-19 and the potential implication of DMARDs in treating this disease.

Iran COVID-19 Immunological Study: &amp;nbsp;Remarkable Level of Interleukin-6 in Iranian COVID-19 Hospitalized Patients

Background: Researchers have already reported a high level of interleukin (IL)-6 in patients affected by coronavirus disease 2019 (COVID-19). In this study, we investigated the surge of IL-6 level and its association with the critical health factors in these patients. Methods: The study sample comprised 111 confirmed hospitalized patients with SARS-CoV-2 and 70 healthy volunteer individuals. Routine laboratory examinations, including hematology, biochemistry, and hormone analysis, as well as IL-6 level measurement, were conducted. Findings: IL-6 levels were significantly high in hospitalized patients compared with healthy individuals (P < 0.001). The IL-6 level was approximately ten-fold of the normal range in 23.7% of the patients and more than 50% of them signify IL-6 over three-fold of normal range. The levels of BS, LDL, VLDL, ALP, TSH, CRP, platelets, neutrophils, and monocytes were significantly different between patients with diverse levels of IL-6. The values of triglyceride, LDL, VLDL, red blood cells and platelets showed an indirect linear trend and the levels of lactate dehydrogenase, serum glutamic oxaloacetic transaminase, creatine phosphokinase, dehydroepiandrosterone sulfate, and CRP demonstrated a direct linear trend with elevating rate of IL-6. Furthermore, IL-6 levels had a significant and direct correlation with troponin I, CRP, ferritin and pro-calcitonin while it had a significant and indirect correlation with VLDL.Interpretation: A hazardous level of IL-6 probably threatening the critical health factors and has a crucial role in immune-mediated acute lung injury in CIOVID-19 patients. Funding Statement: Immunoregulation Research Center of Shahed University Ministry of Health, Treatment and Medical Training of Iran. Declaration of Interests: The authors declare no conflicting of interests. Ethics Approval Statement: The study was approved by the National Ethics Committee on Research in Medical Sciences affiliated to the Iranian Ministry of Health (Ethical Code: IR.NIMAD.REC.1398.411).

STAT4 deficiency fails to induce lung Th2 or Th17 immunity following primary or secondary respiratory syncytial virus (RSV) challenge but enhances the lung RSV-specific CD8+ T cell immune response to secondary challenge.

Immune-mediated lung injury is a hallmark of lower respiratory tract illness caused by respiratory syncytial virus (RSV). STAT4 plays a critical role in CD4+ Th1 lineage differentiation and gamma interferon (IFN-γ) protein expression by CD4+ T cells. As CD4+ Th1 differentiation is associated with negative regulation of CD4+ Th2 and Th17 differentiation, we hypothesized that RSV infection of STAT4-/- mice would result in enhanced lung Th2 and Th17 inflammation and impaired lung Th1 inflammation compared to wild-type (WT) mice. We performed primary and secondary RSV challenges in WT and STAT4-/- mice and used STAT1-/- mice as a positive control for the development of RSV-specific lung Th2 and Th17 inflammation during primary challenge. Primary RSV challenge of STAT4-/- mice resulted in decreased T-bet and IFN-γ expression levels in CD4+ T cells compared to those of WT mice. Lung Th2 and Th17 inflammation did not develop in primary RSV-challenged STAT4-/- mice. Decreased IFN-γ expression by NK cells, CD4+ T cells, and CD8+ T cells was associated with attenuated weight loss and enhanced viral clearance with primary challenge in STAT4-/- mice compared to WT mice. Following secondary challenge, WT and STAT4-/- mice also did not develop lung Th2 or Th17 inflammation. In contrast to primary challenge, secondary RSV challenge of STAT4-/- mice resulted in enhanced weight loss, an increased lung IFN-γ expression level, and an increased lung RSV-specific CD8+ T cell response compared to those of WT mice. These data demonstrate that STAT4 regulates the RSV-specific CD8+ T cell response to secondary infection but does not independently regulate lung Th2 or Th17 immune responses to RSV challenge. STAT4 is a protein critical for both innate and adaptive immune responses to viral infection. Our results show that STAT4 regulates the immune response to primary and secondary challenge with RSV but does not restrain RSV-induced lung Th2 or Th17 immune responses. These findings suggest that STAT4 expression may influence lung immunity and severity of illness following primary and secondary RSV infections.

Severe acute respiratory syndrome (SARS): lessons learnt in Hong Kong.

Many healthcare workers were infected while looking after the SARS patients on the medical wards in 2003. The high infectivity of the SARS coronavirus with peak viral load on day 10 of illness when patients were ill, overcrowding of the old medical wards with low air changes/hr (ACH), and aerosol-generating procedures while resuscitating the patients were the major factors. Procedures reported to present an increased risk of SARS transmission include tracheal intubation, non-invasive ventilation, tracheotomy and manual ventilation before intubation whereas oxygen therapy and bed distance <1 m were also implicated. Studies based on laser visualization technique with smoke particles as smokers in the human patient simulator has shown that oxygen therapy via Hudson mask and nasal cannula could disperse exhaled air of patients to 0.4 and 1 m respectively whereas jet nebulizer could disperse exhaled air >0.8 m from the patient. Bigger isolation rooms with 16 ACH are more effective than smaller isolation rooms with 12 ACH in removing exhaled air and preventing room contamination but at the expense of more noise and electricity consumption. Non-invasive ventilation via face masks and single circuit can disperse exhaled air from 0.4 to 1 m. Both higher inspiratory pressures and use of whisper swivel device (to facilitate carbon dioxide removal) could increase the exhaled air leakage and isolation room contamination during on-invasive ventilation. Addition of a viral-bacterial filter during manual ventilation by bagging may reduce the exhaled air leakage forward and yet increase the sideway leakage. N95 mask was more effective than surgical mask in preventing expelled air leakage during patient's coughing but there was still significant sideway leakage to 15 cm. Clinicians should be aware of air leakage from the various face masks and adopt strict infection control measures during resuscitation of patients with severe respiratory infections. Carefully designed clinical trials are required to determine the optimal timing and dosage of any antiviral agents, convalescent plasma, and immuno-modulating agents in the treatment of the possibly immune-mediated lung injury in SARS and newly emerged infection such as the Middle East Respiratory Syndrome.

Profil étiologique des pleurésies métastatiques

Immune checkpoint inhibitors (ICIs) are newer, immunotherapy-based drugs that have been shown to improve survival in advanced non-small cell lung cancer (NSCLC). Unlike traditional chemotherapeutic agents, ICIs work by boosting the body’s natural tumor killing response. However, this unique mechanism of action has also led to the recognition of class-specific side effects. Labeled immune-related adverse events, these toxicities can affect multiple organ systems including the lungs. Immune-mediated lung injury because of ICI use, termed checkpoint inhibitor pneumonitis (CIP), occurs in about 3% to 5% of patients receiving ICIs; however, the real-world incidence of this entity may be higher, especially now that ICIs are being used in nonclinical trial settings. In this review, we briefly introduce the biology of ICIs and the indications for ICI use in NSCLC and then discuss the epidemiology and clinical and radiologic manifestations of CIP. Next, we discuss management strategies for CIP, including the current consensus on management of steroid-refractory CIP. Given the nascent nature of this field, we highlight areas of uncertainty and emerging research questions in the burgeoning field of checkpoint inhibitor pulmonary toxicity.

Role of Toll-Like Receptor 4 on Lupus Lung Injury and Atherosclerosis in LPS-Challenge ApoE−/−Mice

To investigate the pathologic mechanisms of toll-like receptor 4 (TLR4) in lung injury and atherosclerosis, ApoE−/− or wild-type mice were intraperitoneally administered saline, lipopolysaccharides (LPS), or LPS plus TAK-242 (TLR4 inhibitor), respectively, twice a week for 4 weeks. Serum autoantibody of antinuclear antibody (ANA), anti-double-stranded DNA (anti-dsDNA), and cytokines of interferon-gamma (IFN-γ), tumor necrosis factor (TNF-α), and interleukin-1 (IL-1β) were assessed by ELISA. Hematoxylin and eosin (HE) and Perl's stains for lung pathomorphology as well as HE staining for atherosclerosis were employed. TLR4 in macrophages was detected by double immunofluorescent staining. While protein expressions of TLR4, nuclear factor-kappa B p65 (NF-κB p65), and B cell activating factor belonging to the TNF family (BAFF) were examined by immunohistochemistry. We found that serum autoantibody (ANA and anti-dsDNA), cytokines (IFN-γ, TNF-α, IL-1β), lung inflammation, and intima-media thickness in brachiocephalic artery were obviously increased after LPS challenge in both genotypes, but to a lesser extent in wild-type strains. And those alterations were alleviated by coadministration of LPS and TAK-242. Mechanistically, upregulation of TLR4, NF-κb, and BAFF was involved. We concluded that TLR4/NF-κb/BAFF in macrophages might be a possible common autoimmune pathway that caused lung injury and atherosclerosis. TLR4 signal will be a therapeutic target in atherosclerosis and immune-mediated lung injury.

IFN-γ Receptor-Deficient Donor T Cells Mediate Protection from Graft-versus-Host Disease and Preserve Graft-versus-Tumor Responses after Allogeneic Bone Marrow Transplantation

Graft-versus-host disease (GVHD) is a major complication of allogeneic bone marrow transplantation. It has been previously reported that lung GVHD severity directly correlates with the expansion of donor Th17 cells in the absence of IFN-γ. However, the consequence of Th17-associated lung GVHD in the presence of IFN-γ has not been well characterized. In the current study, T cells from IFN-γ receptor knockout (IFN-γR(-/-)) mice, capable of producing IFN-γ but unable to signal in response to IFN-γ, have been used to elucidate further the role of IFN-γ in GVHD. We found the transfer of donor T cells from either IFN-γR(-/-) or IFN-γ knockout (IFN-γ(-/-)) mice resulted in significant increases in donor Th17 cells in the lung. Marked increases in IL-4-producing Th2 cells infiltrating the lungs were also observed in the mice of donor IFN-γR(-/-) T cells. Notably, despite the presence of these cells, these mice did not show the severe immune-mediated histopathological lung injury observed in mice receiving donor IFN-γ(-/-) T cells. Increases in lung GVHD did occur in mice with donor IFN-γR(-/-) T cells when treated in vivo with anti-IFN-γ demonstrating that the cytokine has a protective role on host tissues in GVHD. A survival benefit from acute GVHD was also observed using donor cells from IFN-γR(-/-) T cells compared with control donors. Importantly, tumor-bearing mice receiving IFN-γR(-/-) T cells versus wild-type donor T cells displayed similar graft-versus-tumor (GVT) effects. These results demonstrate the critical role of IFN-γ on host tissues and cell effector functions in GVHD/GVT.

Immune modulation enhances the macrophage-mediated clearance of Pneumocystis without the severe inflammatory consequences of Pneumocystis pneumonia. (42.11)

Abstract Pneumocystis (Pc) causes high mortality Pneumocystis pneumonia (PcP) in immunocompromised patients. The Pc-driven immune response is essential for host defense against Pc. However, this response is also a key pathologic component of Immune Reconstitution Inflammatory Syndrome (IRIS), an acute form of PcP. NF-κB signaling is critical to many aspects of immune function and inflammatory responses. Its role in regulating immune-mediated inflammatory lung injury, however, is unknown. We hypothesized that specifically interrupting this pathway would diminish the Pc-driven immune response, resulting in reduced inflammatory disease at the expense of impaired immunity. As expected, when Pc-infected immunodeficient mice were immunologically reconstituted they exhibited the marked pulmonary inflammation and rapid respiratory decompensation characteristic of IRIS. In contrast, mice treated with sulfasalazine (SSZ), a potent inhibitor of IκB kinase, showed attenuated pulmonary inflammation and dramatic physiologic improvement. Unexpectedly, SSZ did not abrogate but actually enhanced the clearance of Pc from the host, while promoting an accelerated resolution of inflammatory lung disease. The enhanced Pc clearance is associated with the increased AM phagocytosis. These results suggest that a divergence exists between the mechanisms of lung injury and host defense. NF-κB and AM are potentially important therapeutic targets for the treatment of PcP.

Pneumocystisstimulates MCP-1 production by alveolar epithelial cells through a JNK-dependent mechanism

Pneumocystis carinii is an opportunistic fungal pathogen that causes pneumonia (PCP) in immunocompromised individuals. Recent studies have demonstrated that the host's immune response is clearly responsible for the majority of the pathophysiological changes associated with PCP. P. carinii interacts closely with alveolar epithelial cells (AECs); however, the nature and pathological consequences of the epithelial response remain poorly defined. Monocyte chemotactic protein-1 (MCP-1) is involved in lung inflammation, immunity, and epithelial repair and is upregulated during PCP. To determine whether AECs are an important source of MCP-1 in the P. carinii-infected lung, in vivo and in vitro studies were performed. In situ hybridization showed that MCP-1 mRNA was localized to cells with morphological characteristics of AECs in the lungs of infected mice. In vitro studies demonstrated that P. carinii stimulated a time- and dose-dependent MCP-1 response in primary murine type II cells that was preceded by JNK activation. Pharmacological inhibition of JNK nearly abolished P. carinii-stimulated MCP-1 production, while ERK, p38 MAPK, and TNF receptor signaling were not required. Furthermore, delivery of a JNK inhibitory peptide specifically to pulmonary epithelial cells using a recombinant adenovirus vector blocked the early lung MCP-1 response following intratracheal instillation of infectious P. carinii. JNK inhibition did not affect P. carinii-stimulated production of macrophage inflammatory protein-2 in vitro or in vivo, indicating that multiple signaling pathways are activated in P. carinii-stimulated AECs. These data demonstrate that AECs respond to P. carinii in a proinflammatory manner that may contribute to the generation of immune-mediated lung injury.

Contribution of T cell subsets to the pathophysiology ofPneumocystis-related immunorestitution disease

Immune-mediated lung injury is an important component of Pneumocystis pneumonia (PcP)-related immunorestitution disease (IRD). However, the individual contribution of CD4(+) and CD8(+) T cells to the pathophysiology of IRD remains undetermined. Therefore, IRD was modeled in severe combined immunodeficient mice, and specific T cell depletion was used to determine how T cell subsets interact to affect the nature and severity of disease. CD4(+) cells were more abundant than CD8(+) cells during the acute stage of IRD that coincided with impaired pulmonary physiology and organism clearance. Conversely, CD8(+) cells were more abundant during the resolution phase following P. carinii clearance. Depletion of CD4(+) T cells protected mice from the acute pathophysiology of IRD. However, these mice could not clear the infection and developed severe PcP at later time points when a pathological CD8(+) T cell response was observed. In contrast, mice depleted of CD8(+) T cells efficiently cleared the infection but developed more severe disease, an increased frequency of IFN-gamma-producing CD4(+) cells, and a prolonged CD4(+) T cell response than mice with both CD4(+) and CD8(+) cells. These data suggest that CD4(+) T cells mediate the acute respiratory disease associated with IRD. In contrast, CD8(+) T cells contributed to neither lung injury nor organism clearance when CD4(+) cells were present, but instead served to modulate CD4 function. In the absence of CD4(+) cells, CD8(+) T cells produced a nonprotective, pathological immune response. These data suggest that the interplay of CD4(+) and CD8(+) T cells affects the ultimate outcome of PcP-related IRD.