Analysis of cytokine mRNA profiles in the lungs of Pneumocystis carinii-infected mice

Pneumocystis murina lesions in lungs of experimentally infected Cd40l-/- mice

The Cd40l-/- mouse is a well-established model of X-linked hyper-immunoglobulin M (IgM) syndrome, an immunodeficiency disorder of human beings characterized by the lack of expression of the CD40 ligand (CD40L) on activated T-cells, predisposing to infections with opportunistic pathogens like Pneumocystis jirovecii. The aim of our study was to describe the pulmonary lesions in Cd40l-/- mice experimentally infected with Pneumocystis murina, in comparison with naturally infected severe combined immunodeficient (SCID) mice. Formalin-fixed paraffin-embedded lungs from 26 Cd40l-/-, 11 SCID, and 5 uninfected Cd40l-/- mice were examined by histology and immunohistochemistry for the presence of the pathogen and for leukocyte populations (CD3, CD4, CD45R/B220, CD8a, Iba-1, Ly-6G, CD206, MHC II, and NKp46/NCR1). Infection was confirmed by immunohistochemistry in 18/26 (69%) Cd40l-/- mice and in 11/11 (100%) SCID mice. Fourteen out of 26 (54%) Cd40l-/- mice had interstitial pneumonia. Twenty-three out of 26 (88%) Cd40l-/- mice had peribronchiolar/perivascular lymphoplasmacytic infiltrates, rich in B-cells and Mott cells. Acidophilic macrophage pneumonia was additionally found in 20/26 (77%) Cd40l-/- mice. Only 4/11 (36%) SCID mice had interstitial pneumonia, but no peribronchiolar/perivascular infiltrates or acidophilic macrophage pneumonia were observed in this strain. This study represents the first description of pulmonary histopathological lesions in Cd40l-/- mice infected with P. murina. We speculate that the singular characteristics of the inflammatory infiltrates observed in Cd40l-/- mice could be explained by the specific immune phenotype of the model.

Gene Expression in Lung Epithelial Cells Following Interaction with Pneumocystis carinii and its Specific Life Forms Yields Insights into Host Gene Responses to Infection

Pneumocystis spp. interacts with epithelial cells in the alveolar spaces of the lung. It is thought that the binding of Pneumocystis to host cell epithelium is needed for life cycle completion and proliferation. The effect of this interaction on lung epithelial cells have previously shown that the trophic form of this organism greatly inhibits p34 ^cdc2 activity, a serine/threonine kinase required for transition from G₂ to M phase in the cell cycle. To gain further insight into the host response during Pneumocystis pneumonia (PCP), we used microarray technology to profile epithelial cell (A549) gene expression patterns following Pneumocystis carinii interaction. Furthermore, we isolated separate populations of cyst and trophic forms of P. carinii, which were then applied to the lung epithelial cells. Differential expression of genes involved in various cellular functions dependent on the specific P. carinii life form in contact with the A549 cell were identified. The reliability of our data was further confirmed by Northern blot analysis on a number of selected up or down regulated transcripts. The transcriptional response to P. carinii was dominated by cytokines, apoptotic, and anti-apoptotic related genes. These results reveal several previously unknown effects of P. carinii on the lung epithelial cell and provide insight into the complex interactions of host and pathogen. This article is protected by copyright. All rights reserved.

Increased mRNA expression of key cytokines among suspected cases of Pneumocystis jirovecii infection

Background

Pneumocystis pneumonia (PCP) is a fatal infectious disease caused by Pneumocystis jirovecii (PJP). The major factor relevant to morbidity and mortality seems to be the host inflammatory reaction. The objective of this study was to evaluate the role of IL-2, IL-4, IL-10, and IL-13 cytokine mRNA expression among suspected P. jirovecii infection.

Methods

This was a cross-sectional analytical study undertaken in Aseer region, Saudi Arabia. One hundred suspected PCP cases and 100 healthy controls were included in the study. Basic clinical manifestations, radiological findings, microbiological and immunological findings were extracted from the hospital records from January 2019 to August 2019, Pneumocystis detection was done by immune-fluorescent staining (IFAT, Gomorimethanamine silver staining (GMSS), Giemsa staining, Toluidine blue O (TBO), and Pneumocystis RT-PCR.

Results

Increased more than 5 fold, 3 fold, 4 fold, and 7 fold of IL-2, IL-4, IL-10, and IL-13 mRNA expression were observed in PCP cases compared to controls. Higher expression of IL-2 mRNA was connected with crept, wheezing and chest X-ray findings like central perihilar infiltrate, patchy infiltrate, consolidation, hilar lymphadenopathy, pneumothorax, pleural effusion which showed higher expression compared to counterpart (p< 0.0001). Higher expression of IL-4 mRNA was found to be significantly associated with weight loss (p=0.002), dyspnea (p=0.003), crept (p=0.01), and chest X-ray findings (p< 0.0001). Significantly increased expression of IL-10 mRNA was observed to be associated with weight loss, dyspnea, night sweats, wheezing, and different findings of chest X-ray compared to their counterparts, whereas, IL-13 mRNA was observed in cases with fever. Suspected cases of PCP confirmed positive by IFTA with higher IL-2, IL-4, and IL-10 mRNA expression compared to negative cases. RT-PCR confirmed PCP cases had significantly higher expression of IL-2, IL-4, and IL-10 as well as IL-13 mRNA compared to negative cases. Positive detected cases by GMSS showed higher IL-2, IL-10 mRNA expression, while Giemsa showed only higher IL-4 mRNA expression compared to negative cases.

Conclusion

Confirmed cases of P. jirovecii showed higher IL-2, IL-4, IL-10, and IL-13 mRNA expression comparatively to negative cases. Increased expression of cytokines may be indicative of infection severity and could help in patients’ management.

Pathological and protective immunity to Pneumocystis infection

Pneumocystis jirovecii is a common opportunistic infection in the HIV-positive population and is re-emerging as a growing clinical concern in the HIV-negative immunosuppressed population. Newer targeted immunosuppressive therapies and the discovery of rare genetic mutations have furthered our understanding of the immunity required to clear Pneumocystis infection. The immune system can also mount a pathologic response against Pneumocystis following removal of immunosuppression and result in severe damage to the host lung. The current review will examine the most recent epidemiologic studies about the incidence of Pneumocystis in the HIV-positive and HIV-negative populations in the developing and developed world and will detail methods of diagnosis for Pneumocystis pneumonia. Finally, this review aims to summarize the known mediators of immunity to Pneumocystis and detail the pathologic immune response leading to Pneumocystis-related immune reconstitution inflammatory syndrome.

Pneumocystis

Since its initial misidentification as a trypanosome some 100 years ago, Pneumocystis has remained recalcitrant to study. Although we have learned much, we still do not have definitive answers to such basic questions as, where is the reservoir of infection, how does Pneumocystis reproduce, what is the mechanism of infection, and are there true species of Pneumocystis? The goal of this review is to provide the reader the most up to date information available about the biology of Pneumocystis and the disease it produces.

Classical versus alternative macrophage activation: the Ying and the Yang in host defense against pulmonary fungal infections

Macrophages are innate immune cells that possess unique abilities to polarize toward different phenotypes. Classically activated macrophages are known to have major roles in host defense against various microbial pathogens, including fungi, while alternatively activated macrophages are instrumental in immune-regulation and wound healing. Macrophages in the lungs are often the first responders to pulmonary fungal pathogens, and the macrophage polarization state has the potential to be a deciding factor in disease progression or resolution. This review discusses the distinct macrophage polarization states and their roles during pulmonary fungal infection. We focus primarily on Cryptococcus neoformans and Pneumocystis model systems as disease resolution of these two opportunistic fungal pathogens is linked to classically or alternatively activated macrophages, respectively. Further research considering macrophage polarization states that result in anti-fungal activity has the potential to provide a novel approach for the treatment of fungal infections.

MyD88 signaling regulates both host defense and immunopathogenesis during pneumocystis infection

The immune response protects against Pneumocystis infection but is also a key component of Pneumocystis pneumonia (PcP)-related immunopathogenesis. Signaling through myeloid differentiation factor 88 (MyD88) is critical for activation of immune pathways downstream of TLRs and IL-1R. To determine whether MyD88 regulates normal host defense against Pneumocystis, nonimmunosuppressed wild-type (WT) and MyD88-deficient mice were infected. MyD88(-/-) mice had higher early Pneumocystis burdens than did WT mice but mounted an effective adaptive immune response and cleared Pneumocystis similarly to WT. However, MyD88(-/-) mice displayed a more intense and prolonged pulmonary immune response than did WT mice. To determine the role of MyD88 in the development of PcP-related immunopathogenesis, WT and MyD88(-/-) mice were rendered susceptible to PcP by depletion of CD4(+) T cells. At 4 wk postinfection, CD4-depleted WT and MyD88(-/-) mice harbored similar organism burdens, but MyD88(-/-) mice were protected from the PcP-related respiratory impairment observed in WT mice. Improved pulmonary physiology in MyD88(-/-) mice correlated with lower lung CCL2 levels and reduced cell recruitment. However, by 5 wk postinfection, the overall health of MyD88(-/-) mice began to deteriorate rapidly relative to WT, with accelerated weight loss, impaired lung function, and exacerbated alveolar inflammation. This physiological decline of MyD88(-/-) mice was associated with increased TNF-α and IFN-γ in the lung, and by the inability to control Pneumocystis burden. Thus, MyD88 is not required for resistance to Pneumocystis infection, but limits the adaptive immune response in immunocompetent mice. In the setting of active PcP, MyD88 signaling contributes to both immunopathogenesis and control of fungal burden.

The importance of pro-inflammatory and anti-inflammatory cytokines in Pneumocystis jirovecii pneumonia

The role of pro-inflammatory and anti-inflammatory cytokines in Pneumocystis jirovecii pneumonia (PcP) of non-AIDS immunocompromised patients remains unclear. We measured the levels of pro-inflammatory cytokines including tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, IL-8, monocyte chemoattractant protein-1 (MCP-1) and anti-inflammatory cytokines including IL-10 and transforming growth factor (TGF)-β1 in bronchoalveolar lavage fluid (BALF) and blood in 36 non-AIDS immunocompromised patients with PcP diagnosed by BAL and explored their clinical importance. The severity of PcP was determined by arterial oxygen tension/fraction of inspired oxygen concentration (PaO2/FiO2) ratio, the need of mechanical ventilation and the death. Twenty-five subjects without evidence of lung abnormality were included as control group. Compared with control group, PcP patients had significantly higher BALF levels of IL-1β, TNF-α, IL-6, IL-8 and MCP-1 and significantly higher blood levels of IL-10, TGF-β1, IL-8, IL-6 and MCP-1. For PcP patients, BALF levels of IL-8, IL-8/IL-10 ratio and IL-8/TGF-β1 ratio and blood levels of IL-8 and IL-8/IL-10 ratio were significantly higher in the patients with PaO2/FiO2 < 200 mmHg than in those with PaO2/FiO2 > 200 mmHg. Similarly, significantly higher BALF levels of IL-8, IL-8/IL-10 ratio, IL-1β/IL-10, IL-1β/TGF-β1 ratio, MCP-1/TGF-β1 ratio and IL-8/TGF-β1 ratio were found in the patients requiring mechanical ventilation and in non-survivors. In summary, an imbalance of pro-inflammatory and anti-inflammatory cytokines in BALF was found in PcP of non-AIDS immunocompromised patients. BALF levels of IL-8, IL-8/IL-10 ratio, IL-1β/IL-10 ratio, IL-1β/TGF-β1 ratio, MCP-1/TGF-β1 ratio and IL-8/TGF-β1 ratio may be of value in assessing the severity of PcP and in predicting the outcome of the patients.

The alveolar epithelial cell chemokine response to pneumocystis requires adaptor molecule MyD88 and interleukin-1 receptor but not toll-like receptor 2 or 4

Pneumocystis is an opportunistic fungal pathogen that causes pneumonia in a variety of clinical settings. An early step in Pneumocystis infection involves the attachment of organisms to alveolar epithelial cells (AECs). AECs produce chemokines in response to Pneumocystis stimulation, but the upstream host-pathogen interactions that activate AEC signaling cascades are not well-defined. MyD88 is an adaptor molecule required for activation of proinflammatory signaling cascades following Toll-like receptor (TLR)-dependent recognition of conserved molecular patterns on pathogens. To determine whether the TLR/MyD88 pathway is required for the AEC chemokine response to Pneumocystis, wild-type (WT) and MyD88-deficient AECs were incubated with Pneumocystis. As expected, WT AECs produced CCL2 and CXCL2 following Pneumocystis stimulation. In contrast, MyD88-deficient AECs were severely impaired in their ability to respond to Pneumocystis. MyD88-deficient AECs did not display Pneumocystis-induced Jun N-terminal protein kinase activation and produced much less chemokine than Pneumocystis-stimulated WT AECs. Using a panel of TLR agonists, primary murine AECs were found to respond vigorously to TLR2 and TLR4 agonists. However, the AEC chemokine response to Pneumocystis did not require TLR2 or TLR4. Surprisingly, the interleukin-1 receptor (IL-1R) was required for an AEC chemokine response to Pneumocystis. The role of MyD88 in early responses during Pneumocystis infection was supported by in vivo studies demonstrating that MyD88-deficient mice showed impaired Pneumocystis-stimulated chemokine production and impaired inflammatory cell recruitment. These data indicate an important role for MyD88 in the AEC inflammatory response to Pneumocystis.

Glycosphingolipids mediate pneumocystis cell wall β-glucan activation of the IL-23/IL-17 axis in human dendritic cells

Pneumocystis species are opportunistic fungal organisms that cause severe pneumonia in immune-compromised hosts, with resultant high morbidity and mortality. Recent work indicates that IL-17 responses are important components of host defense against fungal pathogens. In the present study, we demonstrate that cell-surface β-glucan components of Pneumocystis (PCBG) stimulate human dendritic cells (DCs) to secrete IL-23 and IL-6. These cytokines are well established to stimulate a T helper-17 (Th17) phenotype. Accordingly, we further observe that PCBG-stimulated human DCs interact with lymphocytes to drive the secretion of IL-17 and IL-22, both Th17-produced cytokines. The activation of DCs was shown to involve the dectin-1 receptor with a downstream activation of the Syk kinase and subsequent translocation of both the canonical and noncanonical components of the NF-κB transcription factor family. Finally, we demonstrate that glycosphingolipid-rich microdomains of the plasma membrane participate in the activation of DCs by PCBG through the accumulation of lactosylceramide at the cell surface during stimulation with PCBG. These data strongly support the idea that the β-glucan surface components of Pneumocystis drive the activation of the IL-23/IL-17 axis during this infection, through a glycosphingolipid-initiated mechanism.

Host lung gene expression patterns predict infectious etiology in a mouse model of pneumonia

Background

Lower respiratory tract infections continue to exact unacceptable worldwide mortality, often because the infecting pathogen cannot be identified. The respiratory epithelia provide protection from pneumonias through organism-specific generation of antimicrobial products, offering potential insight into the identity of infecting pathogens. This study assesses the capacity of the host gene expression response to infection to predict the presence and identity of lower respiratory pathogens without reliance on culture data.

Methods

Mice were inhalationally challenged with S. pneumoniae, P. aeruginosa, A. fumigatus or saline prior to whole genome gene expression microarray analysis of their pulmonary parenchyma. Characteristic gene expression patterns for each condition were identified, allowing the derivation of prediction rules for each pathogen. After confirming the predictive capacity of gene expression data in blinded challenges, a computerized algorithm was devised to predict the infectious conditions of subsequent subjects.

Results

We observed robust, pathogen-specific gene expression patterns as early as 2 h after infection. Use of an algorithmic decision tree revealed 94.4% diagnostic accuracy when discerning the presence of bacterial infection. The model subsequently differentiated between bacterial pathogens with 71.4% accuracy and between non-bacterial conditions with 70.0% accuracy, both far exceeding the expected diagnostic yield of standard culture-based bronchoscopy with bronchoalveolar lavage.

Conclusions

These data substantiate the specificity of the pulmonary innate immune response and support the feasibility of a gene expression-based clinical tool for pneumonia diagnosis.

Novel therapeutic strategies for acute lung injury induced by lung damaging agents: the potential role of growth factors as treatment options

The increasing threat from terrorism has brought attention to the possible use of toxic industrial compounds (TICs) and other lung-damaging agents as weapons against civilian populations. The way in which these agents could be used favours the development of generic countermeasures. Improved medical countermeasures would increase survivability and improve the quality of recovery of lung damaged casualties. It is evident that there is a dearth of therapeutic regimes available to treat those forms of lung damage that currently require intensive care management. It is quite possible that mass casualties from a terrorist incident or major industrial accident involving the release of large quantities of inhaled TICs would place a severe burden on already scarce intensive care facilities. The development of effective pharmacological approaches to assist the recovery of casualties suffering from acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) may improve the prognosis of such patients (which is currently poor) and would ideally be used as a means of preventing subjects from developing the pulmonary oedema characteristic of ALI/ARDS. Many promising candidate pharmacological treatments have been evaluated for the treatment of ALI/ARDS, but their clinical value is often debatable. Thus, despite improvements in ventilation strategies, pharmacological intervention for ALI/ARDS remains problematical. A new approach is clearly required for the treatment of patients with severely compromised lungs. Whilst the pathology of ALI/ARDS associated with exposure to a variety of agents is complex, numerous experimental studies suggest that generic therapeutic intervention directed at approaches that aim to upregulate repair of the damaged alveolar blood/air barrier of the lung may be of value, particularly with respect to chemical-induced injury. To this end, keratinocyte growth factor (KGF), epithelial growth factor (EGF) and basic fibroblast growth factor (bFGF) are emerging as the most important candidates. Hepatocyte growth factor (HGF) does not have epithelial specificity for lung tissue. However, the enhanced effects of combinations of growth factors, such as the synergistic effect of HGF upon vascular endothelial growth factor (VEGF)-mediated endothelial cell activity, and the combined effect of HGF and KGF in tissue repair should be investigated, particularly as the latter pair of growth factors are frequently implicated in processes associated with the repair of lung damage. Synergistic interactions also occur between trefoil factor family (TFF) peptides and growth factors such as EGF. TFF peptides are most likely to be of value as a short term therapeutic intervention strategy in stimulating epithelial spreading activities which allow damaged mucosal surfaces to be rapidly covered by epithelial cells.

Cellular and cytokine changes in the alveolar environment among immunocompromised patients during Pneumocystis jirovecii infection

Limited data exist on the cytokine and cellular changes in the alveolar environment in immunocompromised patients during Pneumocystis jirovecii infection. A cellular and a cytokine analysis were performed on bronchoalveolar lavage (BAL) samples from three groups of patients, i.e., an initial study group of 64 immunocompromised P. jirovecii-positive individuals and two control groups of P. jirovecii-negative patients who had been or not immunosuppressed (65 patients). The results were related to alveolar dilution as determined by urea measurement. Compared with non-infected groups, P. jirovecii-infected patients had a lower level of alveolar macrophages (AM), particularly those with high burdens of P. jirovecii. Alveolar macrophages over-expressed the Dectin-1 receptor, which was largely implicated in P. jirovecii clearance. The alveolar CD8+T and CD4+T lymphocyte counts were increased and an inverse correlation was observed between the alveolar CD4+ cell count and the P. jirovecii burden. Although the alveolar IL-6 level was considerably increased, alveolar IL-17, IL-10, TNF-α, TGF-β concentrations of P. jirovecii patients were not different from the control groups. Changes in the pulmonary environment were also highlighted during P. jirovecii colonization. Our study suggests that there is a correlation between the P. jirovecii burden in the alveolus (from colonization to a high P. jirovecii burden), and the degree of impairment of the alveolar immune response.

Neuritogenic effects of T cell-derived IL-3 on mouse splenic sympathetic neurons in vivo

To determine the role played by lymphocytes and cytokines in the growth of sympathetic neurons in vivo, the innervation and cytokine levels were examined in the spleens of SCID mice that lack T and B cells. Splenic noradrenaline, nerve growth factor (NGF), and IL-1beta levels were elevated in SCID mice. Immunohistochemical examination revealed that the density of tyrosine hydroxylase-positive (TH(+)) fibers of splenic central arteries in SCID mice was increased compared with wild-type C.B-17 mice, while SCID mice had significantly fewer TH(+) fibers in their periarteriolar lymphatic sheaths (PALS). Two weeks after SCID mice were injected with C.B-17 splenic T cells, their TH(+) fiber staining increased in the PALS. IL-3 levels increased significantly in SCID mice following T cell reconstitution, and the administration of anti-IL-3 Ab blocked the above T cell-induced increase in innervation in the PALS. Anti-IL-3 treatment also inhibited the regeneration of splenic sympathetic neurons in C.B-17 mice after they were chemically sympathetomized with 6-hydroxydopamine. Depletion of NK cells by anti-asialo GM1 promoted the splenic innervation in SCID mice, while there were no significant changes in the innervation between CD8(+) T cell-deficient beta(2)-microglobulin knockout mice and their wild type. Our results suggest that T cells (probably CD4(+) Th cells but not CD8(+) CTLs) play a role in regulating the sympathetic innervation of the spleen; this effect appeared to be mediated, at least in part, by IL-3. On the contrary, NK cells may exert an inhibitory effect on the sympathetic innervation.

Pneumocystis: a novel pathogen in chronic obstructive pulmonary disease?

Chronic obstructive pulmonary disease (COPD) results in significant morbidity and mortality. Smoking has long been recognized as the primary risk factor for development of COPD, but factors determining the severity or pattern of disease in smokers are largely unknown. Recent interest has focused on the potential role of infectious agents and the associated host response in accelerating progression of airway obstruction or in perpetuating its progression following discontinuation of tobacco exposure. Pneumocystis jirovecii is a fungal pathogen that causes pneumonia in immunocompromised individuals. Recent evidence has linked this organism with COPD. Using sensitive molecular techniques, low levels of Pneumocystis have been detected in the respiratory tract of certain individuals and termed colonization. Several findings support the theory that colonization with Pneumocystis is involved in the "vicious circle" hypothesis of COPD in which colonization with organisms perpetuates an inflammatory and lung remodeling response. Pneumocystis colonization is more prevalent in smokers and in those with severe COPD. The presence of Pneumocystis in the lungs, even at low levels, produces inflammatory changes similar to those seen in COPD, with increases in numbers of neutrophils and CD8(+) lymphocytes. HIV-infected subjects who have had PCP develop permanent airway obstruction, and HIV-infected patients have a high prevalence of both emphysema and Pneumocystis colonization. In addition, a non-human primate model of colonization shows development of airway obstruction and radiographic emphysema. Additional studies are needed to confirm the role of Pneumocystis in the pathogenesis of COPD, given that this agent might be a treatable co-factor in disease progression.

Animal models: an important tool in mycology

Animal models of fungal infections are, and will remain, a key tool in the advancement of the medical mycology. Many different types of animal models of fungal infection have been developed, with murine models the most frequently used, for studies of pathogenesis, virulence, immunology, diagnosis, and therapy. The ability to control numerous variables in performing the model allows us to mimic human disease states and quantitatively monitor the course of the disease. However, no single model can answer all questions and different animal species or different routes of infection can show somewhat different results. Thus, the choice of which animal model to use must be made carefully, addressing issues of the type of human disease to mimic, the parameters to follow and collection of the appropriate data to answer those questions being asked. This review addresses a variety of uses for animal models in medical mycology. It focuses on the most clinically important diseases affecting humans and cites various examples of the different types of studies that have been performed. Overall, animal models of fungal infection will continue to be valuable tools in addressing questions concerning fungal infections and contribute to our deeper understanding of how these infections occur, progress and can be controlled and eliminated.

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.

Toll-like receptor 2 mediates alveolar macrophage response to Pneumocystis murina

The innate immune response to Pneumocystis infection is not well understood. In this study, normal C57BL/6 mouse alveolar macrophages were found to respond to Pneumocystis murina organisms through Toll-like receptor 2 (TLR2), leading to the nuclear translocation of NF-kappaB and the production of proinflammatory cytokine tumor necrosis factor alpha (TNF-alpha) and chemokine macrophage inflammatory protein 2 (MIP-2). P. murina stimulation of normal alveolar macrophages from C57BL/6 mice resulted in increased TLR2 transcription but not increased TLR4 transcription. In gain-of-function studies with HEK293 cells expressing TLR2 or TLR4, only TLR2 was found to stimulate an NF-kappaB response to P. murina. TNF-alpha and MIP-2 production in response to P. murina by mouse alveolar macrophages was inhibited by a monoclonal antibody that specifically blocked the ligand-binding ability of TLR2. Alveolar macrophages from TLR2 knockout (TLR2-/-) mice showed little increase in TNF-alpha and MIP-2 mRNA levels upon P. murina stimulation. An in vivo study showed that TLR2-/- mice challenged with P. murina had reduced cytokine responses. These results indicate that TLR2 plays a major role in the innate immune response to P. murina.

CD8 T cell-mediated lung damage in response to the extracellular pathogen pneumocystis is dependent on MHC class I expression by radiation-resistant lung cells

Pneumocystis, a fungal, extracellular pathogen causes a life-threatening pneumonia in patients with severe immunodeficiencies. In the absence of CD4 T cells, Pneumocystis infection results in vigorous CD8 T cell influx into the alveolar and interstitial spaces of the lung. This response results in lung damage characterized by low pO2 and albumin leakage into the bronchoalveolar lavage fluid similar to other CD8 T cell-mediated interstitial lung diseases. How this extracellular pathogen elicits a CD8 T cell response is not clear, and it was the aim of our study to determine the Ag specificity of the recruited CD8 T cells and to determine whether MHC class I (MHC I) expression was necessary to initiate lung damage. Using an adoptive T cell-transfer model with either polyclonal wild-type CD8 T cells or transgenic influenza virus-specific CD8 T cells we found that CD8 T cell recruitment is Ag-specific and requires the continuous presence of the Pneumocystis pathogen. Bone marrow chimera experiments using Rag-1 and beta2-microglobulin-deficient mice as hosts demonstrated a requirement for MHC I expression on nonbone marrow-derived cells of the lung. This suggests either direct processing of Pneumocystis Ags by nonbone marrow-derived cells of the lung or the induction of lung damage triggered by a lung-specific autoantigen. Using perforin-, Fas-, and IFN-gamma-deficient animals, we showed that these molecules are not directly involved in the CD8-mediated lung damage. However, CD8 T cell-mediated lung damage is Ag-specific is induced by a MHC I-expressing nonbone marrow-derived cell in the lung and is dependent on the continued presence of live Pneumocystis.

Resolution of Pneumocystis murina infection following withdrawal of corticosteroid induced immunosuppression

The host response during resolution of Pneumocystis murina infection following withdrawal of Dexamethasone (Dex) induced immunosuppression was analyzed. Mice were inoculated with P. murina and treated with Dex for 4 weeks. Treatment was stopped and mice were sacrificed at d1, d7, and d14. Control mice were treated in the same manner, but were inoculated with nonviable P. murina. P. murina was actively cleared from the lungs following withdrawal of Dex treatment. No P. murina was detected in control mice. Significantly more neutrophils, lymphocytes, macrophages, and eosinophils were recovered from the lungs of mice that had been infected with P. murina than from control mice at d7, but only neutrophils remained significantly elevated at d14. Significantly more CD4+ and CD8+ T cells were purified from the lungs of mice that had been infected with P. murina mice at d7 and d14. Cytokine levels were measured in lung lavage fluid by ELISA. TNF-alpha, IFN-gamma, IL-1, and IL-6 levels were higher in mice that had been inoculated with P. murina at all three time points. TNF-alpha and IL-1 levels did not change significantly following withdrawal of Dex treatment. Low levels of IL 6 were detected at d1, but increased significantly by d7 and d14. IFN-gamma levels peaked at d14. Chemokine message levels were measured in lung tissue by ribonuclease protection assay. MIP-1beta and IP-10 message increased between d1 and d7 and then decreased by d14. RANTES message levels increased from d1 to d7 and remained elevated at d14. Withdrawal of Dex induced immunosuppression from P. murina infected mice resulted in activation of many arms of the host response that lead to resolution of the infection.

Pneumocystis carinii infection sensitizes lung to radiation-induced injury after syngeneic marrow transplantation: role of CD4+ T cells

A murine model of bone marrow transplant (BMT)-related lung injury was developed to study how infection sensitizes lung to the damaging effects of total body irradiation (TBI) at infectious and TBI doses that individually do not cause injury. Mice infected with Pneumocystis carinii exhibited an asymptomatic, rapid, and transient influx of eosinophils and T cells in bronchoalveolar lavage fluid (BALF). In contrast, mice infected with P. carinii 7 days before receiving TBI and syngeneic BMT (P. carinii/TBI mice) exhibited severe pulmonary dysfunction, surfactant aggregate depletion, and surfactant activity reductions at 17 days post-BMT. BALF from P. carinii/TBI mice contained a disproportionate initial influx of CD4(+) T cells (CD4(+):CD8(+) ratio of 2.7) that correlated with progressive lung injury (from 8 to 17 days post-BMT). Levels of TNF-alpha in BALF were significantly increased in P. carinii/TBI mice compared with mice given either insult alone, with peak values found at 11 days post-BMT. In vivo depletion of CD4(+) T cells in P. carinii/TBI mice abrogated pulmonary dysfunction and reduced TNF-alpha levels in BALF, whereas depletion of CD8(+) T cells did not affect lung compliance or TNF-alpha. Lung injury was not attributable to direct P. carinii damage, since CD4-depleted P. carinii/TBI mice that exhibited no injury had higher average lung P. carinii burdens than either mice given P. carinii alone or undepleted P. carinii/TBI mice. Together, these results indicate that P. carinii infection can sensitize the lung to subsequent TBI-mediated lung injury via a process dependent on non-alloreactive CD4(+) T cells.

Negative regulatory role of mannose receptors on human alveolar macrophage proinflammatory cytokine release in vitro

Alveolar macrophages (AM) are critical components of lung innate immunity and contribute to an effective host response to Pneumocystis pneumonia. Recognition of unopsonized Pneumocystis organisms by human AM is mediated predominantly via mannose receptors and results in phagocytosis, release of reactive oxygen species, and activation of the nuclear transcription factor (NF)-kappaB. However, the AM host defense genes activated by Pneumocystis have not been defined. In the present study, incubation of AM with unopsonized Pneumocystis organisms was not associated with release of interleukin (IL)-1beta, IL-6, or tumor necrosis factor (TNF)-alpha (important cytokines in the host response to Pneumocystis) and did not induce IL-1beta, IL-6, or TNF-alpha mRNA transcripts. These findings were not attributed to Pneumocystis-induced cytopathic changes, as these same AM released IL-8 and matrix metalloproteinase-9 in response to Pneumocystis. NF-kappaB-mediated IL-8 release was independent of Pneumocystis phagocytosis. The observed response was specific, as IL-1beta, IL-6, and TNF-alpha release and mRNA induction were preserved in response to lipopolysaccharide or serum-opsonized Pneumocystis. The absence of IL-1beta, IL-6, and TNF-alpha release in response to Pneumocystis was predominately influenced by AM mannose receptors, as blocking mannose receptors or targeted mannose receptor small interfering RNA functional gene silencing resulted in TNF-alpha release in response to unopsonized Pneumocystis organisms. Furthermore, ligation of AM mannose receptors by unopsonized Pneumocystis organisms reduced Toll-like receptor 4-mediated TNF-alpha release. Taken together, these data suggest that mannose receptors on human AM may suppress select proinflammatory cytokine release and may serve to regulate the innate inflammatory responses to infectious challenge in the lungs.

Pneumocystis carinii activates the NF-kappaB signaling pathway in alveolar epithelial cells

Pneumocystis carinii pneumonia (PcP) is a clinically important infection of immunocompromised patients. Although the interaction of Pneumocystis with the alveolar epithelium has been well documented, very little information regarding the epithelial response to Pneumocystis is currently available. In order to study Pneumocystis-epithelium interactions, a murine cell line derived specifically from an alveolar epithelial cell (AEC) was utilized. The coculture of murine AECs with mouse Pneumocystis induced a dose- and time-dependent release of the CXC chemokine MIP-2. Importantly, the specific removal of Pneumocystis from the preparation, or the pretreatment of AECs with sulfasalazine, a potent and specific inhibitor of NF-kappaB, nearly completely abrogated the chemokine response to Pneumocystis. Since the murine MIP-2 promoter contains consensus kappaB binding sequences, the ability of Pneumocystis to stimulate NF-kappaB signaling in AECs was examined. Pneumocystis stimulation of an AEC line stably transfected with a kappaB-dependent reporter construct triggered the NF-kappaB signaling pathway and reporter production. These data were confirmed in gel shift assays, providing direct evidence that Pneumocystis induced the nuclear translocation of the p50/p65 heterodimeric form of NF-kappaB. Maximal NF-kappaB activation was dependent upon direct contact with viable Pneumocystis organisms. These data demonstrate that Pneumocystis activates NF-kappaB signaling in AECs and establish a reporter cell line for studying NF-kappaB activation in AECs. Given the global regulatory functions of the NF-kappaB family, these findings suggest that Pneumocystis directly alters AEC gene expression in a manner that promotes pulmonary immune and inflammatory responses.

Surfactant protein A limits Pneumocystis murina infection in immunosuppressed C3H/HeN mice and modulates host response during infection

The development of Pneumocystis murina pneumonia and host response were characterized over time and at different levels of infection in corticosteroid immunosuppressed surfactant protein A (SP-A) knockout and wild-type (WT) mice. Infection increased over time in both strains of mice; however, significantly more cyst forms were detected in the knockout mice at intermediate and late stages of infection. In mice with heavy infections, TNF-alpha and IFN-gamma protein concentrations were significantly higher in pulmonary lavage fluid from knockout mice. There was a significant positive correlation between TNF-alpha and IFN-gamma concentrations and the level of infection in knockout mice, but not in WT mice. No significant differences were detected in IL-1 levels between the two strains of mice at any of the time points or at any level of infection. At heavier infection levels, significantly more MIP-2 protein was detected in the lungs of knockout mice, but a significant positive correlation between MIP-2 concentrations and the infection level was detected in both groups of mice. At the intermediate stage of infection, a significantly higher percentage of neutrophils was detected in the lungs of knockout mice than in WT mice. There was no difference in SP-D levels between WT and KO mice with identical levels of infection. These data support a protective role for SP-A in host defense against Pneumocystis and suggest that the effects of SP-A on the host response vary based on the intensity of the infection.

Pneumocystis cell wall beta-glucans stimulate alveolar epithelial cell chemokine generation through nuclear factor-kappaB-dependent mechanisms

Exuberant inflammatory responses are associated with respiratory failure during Pneumocystis pneumonia. Alveolar epithelial cells (AECs) promote Pneumocystis attachment and proliferation, but also contribute prominently to host cytokine-mediated inflammation during pneumonia. Recent investigations indicate that AECs produce macrophage inflammatory protein-2 (MIP-2) and tumor necrosis factor-alpha (TNF-alpha) following challenge with Pneumocystis carinii. Nuclear factor-kappaB (NF-kappaB) is a ubiquitous transcription factor critical for regulation of proinflammatory cytokine expression. Herein, we assess rat AEC NF-kappaB responses to challenge with a P. carinii beta-glucan cell wall component (PCBG). Prominent nuclear translocation of p65 NF-kappaB was demonstrated following PCBG challenge. NF-kappaB activation was in part mediated through Protein Kinase C (PKC) signaling pathways. PCBG challenge of AECs was also shown to induce MIP-2 and TNF-alpha mRNA production, a response that was ameliorated by NF-kappaB inhibition. MIP-2 protein expression was also dramatically increased by PCBG challenge, in a manner that was significantly attenuated by both PKC and NF-kappaB inhibition. The data further demonstrate that AEC chemokine responses were not mediated by the recently described dectin-1 receptor, but instead involved participation of cell surface lactosylceramide. These data support a significant role for AECs in host responses during Pneumocystis pneumonia, and further indicate that beta-glucan induces inflammatory cytokine production through NF-kappaB-dependent mechanisms.

Pneumocystis activates human alveolar macrophage NF-kappaB signaling through mannose receptors

Alveolar macrophages (AM) represent important effector cells in the innate immune response to the AIDS-related pathogen Pneumocystis, but the early AM host defense signaling events are poorly defined. Using AM from healthy individuals, we showed in the present study that Pneumocystis organisms stimulate AM NF-kappaB p50 and p65 nuclear translocation in a time-dependent and multiplicity-of-infection-dependent manner as determined by electrophoretic mobility shift assay and immunofluorescence microscopy and that NF-kappaB nuclear translocation is associated with I-kappaB phosphorylation. Importantly, competitive inhibition of mannose receptor and targeted short interfering RNA-mediated gene suppression of mannose receptor mRNA and protein is associated with complete elimination of NF-kappaB nuclear translocation in response to Pneumocystis. Furthermore, human immunodeficiency virus (HIV) infection of AM (as a model human disease state of reduced AM mannose receptor expression and function) inhibits Pneumocystis-mediated NF-kappaB nuclear translocation and is associated with reduced I-kappaB phosphorylation and reduced interleukin-8 (IL-8) release. In contrast, NF-kappaB nuclear translocation and IL-8 release in response to lipopolysaccharide are intact in AM from both healthy and HIV-infected individuals, indicating that the observed impairment is not a global disturbance of the NF-kappaB pathway. Thus, in addition to phagocytic and endocytic effector functions, the present study identifies mannose receptors as pattern recognition receptors capable of NF-kappaB activation in response to infectious non-self challenge. AM mannose receptor-mediated NF-kappaB activation may represent an important mechanism of the host cell response to Pneumocystis, and altered NF-kappaB activation in the context of HIV infection may impair a critical innate immune signaling response and may contribute to pathogenesis of opportunistic lung infections.

Sensitized splenocytes result in deleterious cytokine cascade and hyperinflammatory response in rats with Pneumocystis pneumonia despite the presence of corticosteroids

The immune response to the opportunistic pulmonary pathogen Pneumocystis can have beneficial and harmful effects on the host despite the presence of corticosteroids. We hypothesized that this deleterious hyperinflammatory response is associated with exaggerated cytokine production. The adoptive transfer of at least 10(7) immune splenocytes reduced the cyst count in rats with corticosteroid-induced pneumocystosis. About 18% of these rats developed clinical illness, an increased lung weight/body weight (LW/BW) ratio, and elevated levels of interleukin 1alpha (IL-1alpha), IL-1beta, IL-6, tumor necrosis factor alpha, IL-5, IL-10, and gamma interferon in the lungs. This hyperinflammatory reaction was not observed in rats that remained clinically well or in control rats. Thus, in this model, corticosteroids have little effect on the cytokine cascade or other adverse effects of the host immune response to Pneumocystis.

TNF Receptor Signaling Contributes to Chemokine Secretion, Inflammation, and Respiratory Deficits duringPneumocystisPneumonia

CD8(+) T cells contribute to the pathophysiology of Pneumocystis pneumonia (PcP) in a murine model of AIDS-related disease. The present studies were undertaken to more precisely define the mechanisms by which these immune cells mediate the inflammatory response that leads to lung injury. Experimental mice were depleted of either CD4(+) T cells or both CD4(+) and CD8(+) T cells and then infected with Pneumocystis: The CD4(+)-depleted mice had significantly greater pulmonary TNF-alpha levels than mice depleted of both CD4(+) and CD8(+) T cells. Elevated TNF-alpha levels were associated with increased lung concentrations of the chemokines RANTES, monocyte chemoattractant protein 1, macrophage-inflammatory protein 2, and cytokine-induced neutrophil chemoattractant. To determine whether TNFR signaling was involved in the CD8(+) T cell-dependent chemokine response, TNFRI- and II-deficient mice were CD4(+) depleted and infected with Pneumocystis: TNFR-deficient mice had significantly reduced pulmonary RANTES, monocyte chemoattractant protein 1, macrophage-inflammatory protein 2, and cytokine-induced neutrophil chemoattractant responses, reduced inflammatory cell recruitment to the alveoli, and reduced histological evidence of PcP-related alveolitis as compared with infected wild-type mice. Diminished pulmonary inflammation correlated with improved surfactant activity and improved pulmonary function in the TNFR-deficient mice. These data indicate that TNFR signaling is required for maximal CD8(+) T cell-dependent pulmonary inflammation and lung injury during PcP and also demonstrate that CD8(+) T cells can use TNFR signaling pathways to respond to an extracellular fungal pathogen.

New rat model of Pneumocystis pneumonia induced by anti-CD4(+) T-lymphocyte antibodies

The CD4(+) T lymphocyte plays a central role in host defense against Pneumocystis pneumonia but has received only limited attention in rats. CD4(+) T-cell-depleting (OX-38) and nondepleting (W3/25) monoclonal antibodies, which recognize an identical or adjacent epitope, were administered for up to 14 weeks to Lewis rats that had been exposed to PNEUMOCYSTIS: While OX-38 produced a greater decrease in circulating CD4(+) cells than W3/25, both antibody treatments resulted in similar effects on the health of the rats and the levels of Pneumocystis pneumonia, which were milder than those found with corticosteroids. W3/25 also did not enhance the severity of Pneumocystis pneumonia achieved with corticosteroids alone. We conclude that CD4(+) cell function is more important than CD4(+) cell number in host defense against Pneumocystis in the rat and that this new model permits study of opportunistic infections in the rat without the confounding effects of corticosteroids.

T cell costimulatory molecule function determines susceptibility to infection with Pneumocystis carinii in mice

Loss of T cell number and function during HIV infection or secondary to pharmacologic immunosuppression renders individuals susceptible to opportunistic infections, including Pneumocystis carinii pneumonia. Because costimulatory receptors are critical for optimal T cell function, we hypothesized that these proteins would regulate susceptibility to opportunistic infections. We found that despite normal T cell numbers, mice deficient in the costimulatory molecules CD2 and CD28 spontaneously developed P. carinii pneumonia. In experiments using intratracheal injection of P. carinii organisms to induce infection, the loss of CD28 alone was sufficient to render mice susceptible to acute infection; however, the organism was eventually cleared. Examination of inflammatory responses to P. carinii revealed that mice deficient in both CD2 and CD28 accumulated CD8(+) T cells in their lungs in response to infection and demonstrated markedly reduced specific Ab titers. Analysis of cytokine profiles suggested that regulation of IL-10 and IL-15 may be important elements of the response to this pathogen. Thus, costimulatory molecule function is critical in determining the initial susceptibility to infection with P. carinii. Analysis of immunologic responses in these mice may provide important insights into the defects that render individuals susceptible to opportunistic infection, and provide opportunities for novel immunologically based therapies.

Exposure of immunocompetent adult mice to Pneumocystis carinii f. sp. muris by cohousing: growth of P. carinii f. sp. muris and host immune response

There has been emerging evidence that immunocompetent hosts can harbor Pneumocystis in their lungs. The purpose of this study was to determine the kinetics of Pneumocystis carinii f. sp. muris infection in adult immunocompetent mice and the host immune response to the organisms. To accomplish this, we exposed adult immunocompetent mice to SCID mice infected with P. carinii f. sp. muris by cohousing. We found that P. carinii f. sp. muris was detectable in the lungs of cohoused immunocompetent mice by PCR by 3 weeks after the beginning of cohousing. At about 4 weeks of cohousing, P. carinii f. sp. muris was readily detectable in the lungs of mice by microscopic techniques. Also at this time, P. carinii f. sp. muris-specific immunoglobulin G was found in the sera of the mice, and CD62(low) CD4- and CD8-positve T cells accumulated in the lungs. Shortly after this immune response, the P. carinii f. sp. muris organisms were cleared from the lungs. Adult mice cohoused for only 1 week also contained P. carinii f. sp. muris cysts detectable by silver staining at 5 and 6 weeks after the beginning of cohousing. We also found that the P. carinii f. sp. muris organisms grew to greater numbers in the lungs of BALB/c mice than in those of C57BL6 mice. This indicates that immunocompetent hosts develop a mild infection with P. carinii f. sp. muris which resolves in 5 to 6 weeks when there is a detectable immune response to the organism. Once an acquired immune response was initiated, the P. carinii f. sp. muris organisms were quickly eliminated without clinical signs of disease.

IL-10 modulates host responses and lung damage induced by Pneumocystis carinii infection

Host responses to Pneumocystis carinii infection mediate impairment of pulmonary function and contribute to the pathogenesis of pneumonia. IL-10 is known to inhibit inflammation and reduce the severity of pathology caused by a number of infectious organisms. In the present studies, IL-10-deficient (IL-10 knockout (KO)) mice were infected with P. carinii to determine whether the severity of pathogenesis and the efficiency of clearance of the organisms could be altered in the absence of IL-10. The clearance kinetics of P. carinii from IL-10 KO mice was significantly enhanced compared with that of wild-type (WT) mice. This corresponded to a more intense CD4(+) and CD8(+) T cell response as well as an earlier neutrophil response in the lungs of IL-10 KO mice. Furthermore, IL-12, IL-18, and IFN-gamma were found in the bronchoalveolar lavage fluids at earlier time points in IL-10 KO mice suggesting that alveolar macrophages were activated earlier than in WT mice. However, when CD4(+) cells were depleted from P. carinii-infected IL-10 KO mice, the ability to enhance clearance was lost. Furthermore, CD4-depleted IL-10 KO mice had significantly more lung injury than CD4-depleted WT mice even though the intensity of the inflammatory responses was similar. This was characterized by increased vascular leakage, decreased oxygenation, and decreased arterial pH. These data indicate that IL-10 down-regulates the immune response to P. carinii in WT mice; however, in the absence of CD4(+) T cells, IL-10 plays a critical role in controlling lung damage independent of modulating the inflammatory response.

Radiation-induced pulmonary fibrosis: examination of chemokine and chemokine receptor families

Fibrosis is a common outcome of chronic inflammation or injury. Pulmonary fibrosis may be the result of abnormal repair after an acute inflammatory response. The process of repair initiated by a tissue insult is largely a function of the activation of cells to produce important biological mediators such as cytokines, growth factors and chemokines, which orchestrate most aspects of the inflammatory response. Consequently, altered regulation of the production of inflammatory cell cytokines and chemokines after injury and repair likely contributes to the fibrosis. Our hypothesis is that chronic expression of specific chemokine and chemokine receptors during the fibrotic phase induced by thoracic irradiation may perpetuate the recruitment and activation of lymphocytes and macrophages, which may contribute to the development of fibrosis. Fibrosis-sensitive (C57BL/6) and fibrosis-resistant (C3H/HeJ) mice were irradiated with a single dose of 12.5 Gy to the thorax. Total lung RNA was prepared and hybridized using microarray analysis and RNase protection assays. At 26 weeks postirradiation, messages encoding the chemokines BLC (now known as Scyb13), C10 (now known as Scya6), IP-10 (now known as Scyb10), MCP-1 (now known as Scya2), MCP-3 (now known as Scya7), MIP-1gamma (now known as Scya9), and RANTES (now known as Scya5) and the chemokine receptors Ccr1, Ccr2, Ccr5 and Ccr6 were elevated in fibrosis-sensitive (C57BL/6) mice. In contrast, only the messages encoding SDF-1alpha (now known as Sdf1) and Ccr1 were elevated 26 weeks postirradiation in fibrosis-resistant (C3H/HeJ) mice. Our results point to the CC and CCR family members as the predominant chemokine responders during the development of fibrosis. These studies suggest that monocyte/macrophage and lymphocyte recruitment and activation are key components of radiation-induced fibrosis.

Vitronectin and fibronectin function as glucan binding proteins augmenting macrophage responses to Pneumocystis carinii

beta-glucans represent major structural components of fungal cell walls. We recently reported that Pneumocystis carinii beta-glucans stimulate alveolar macrophages to release proinflammatory cytokines. Macrophage activation by beta-glucan is augmented by serum, implying the presence of circulating factors that interact with beta-glucans and enhance their ability to stimulate macrophages. Using beta-glucan-enriched cell wall fractions from P. carinii and Saccharomyces cerevisiae, two prominent proteins were precipitated from serum and demonstrated to be vitronectin (VN) and fibronectin (FN) by immune analysis. Preincubation of beta-glucan with VN or FN enhanced macrophage activation in response to this cell wall component. Because VN and FN accumulate in the lungs during P. carinii pneumonia, we further investigated hepatic and pulmonary expression of VN and FN messenger RNA during infection. P. carinii pneumonia in rodents is associated with increased hepatic expression of VN and FN as well as increased local expression of FN in the lung. Because interleukin (IL)-6 represents the major regulator of VN and FN expression during inflammatory conditions, we measured macrophage IL-6 release in response to stimulation with P. carinii beta-glucan. Stimulation of macrophages with P. carinii beta-glucan induced significant release of IL-6. Elevated concentrations of IL-6 were noted in the blood of infected animals compared with uninfected control animals. These studies indicate that VN and FN bind to beta-glucan components of P. carinii and augment macrophage inflammatory responses. P. carinii cell wall beta-glucan stimulates secretion of IL-6 by macrophages, thereby enhancing hepatic synthesis of both VN and FN, and lung synthesis of FN during pneumonia.

Role of chemokines in fungal infections

The production of chemokines at the site of a fungal infection is critical for effective recruitment of leukocytes to that site. Over 40 chemokines and 20 chemokine receptors have been identified. The most intriguing biological property of chemokines is that they often play non-redundant roles in vivo even though they are highly related, have multiple activities and bind multiple chemokine receptors. Almost all of the chemokine studies to date have concentrated on responses to Cryptococcus, Candida, Aspergillus or Pneumocystis. The role of chemokines in infections caused by fungi such as Histoplasma, Blastomyces, Coccidioides and Paracoccidioides remains to be explored. In this review we have summarized what is currently known about the role of chemokines during fungal infection, including the influence of these signaling proteins on effector cell recruitment and development of cell-mediated immunity.

Delayed inflammatory response to Pneumocystis carinii infection in neonatal mice is due to an inadequate lung environment

Challenge of neonatal mice with an intranasal inoculation of Pneumocystis carinii results in a subclinical infection that takes 6 wk to resolve, whereas adult mice resolve a comparable challenge within 3 wk. This delayed clearance is due to a delayed inflammatory response in neonatal mice; however, the reason for this delay has been unknown. To determine whether the neonatal lung environment is sufficient to attract immunocompetent lymphocytes into the lungs, an adoptive transfer strategy was employed in which splenocytes from adult BALB/c mice were transferred into P. carinii-infected neonatal or adult SCID mice. All adults, but no pups, resolved their infections by day 37 postreconstitution. Despite reconstitution with adult splenocytes, pups had a negligible lung inflammatory response until day 24, whereas adult mice had activated CD4(+) and CD8(+) cells in the lung by day 13. The delay in neonates corresponded to delayed kinetics of expression of lung cytokines TNF-alpha and IFN-gamma mRNA and chemokines lymphotactin, RANTES, and macrophage inflammatory protein-1ss mRNA. Phagocytic cells from neonatal mice were significantly less efficient than adult cells at migrating to the draining lymph nodes after phagocytosing fluorescent beads. There were fewer dendritic cells and Ia(+) myeloid cells in the lungs of P. carinii-infected neonatal mice compared with adults. These data indicate that the lung environment of neonatal mice is insufficient for migration of T cells, due at least in part to inefficient phagocytosis and migration of APCs to the lymph nodes as well as delayed chemokine and TNF-alpha mRNA expression.

Cell type-specific regulation of fibrinogen expression in lung epithelial cells by dexamethasone and interleukin-1beta

Our recent studies demonstrating the expression of fibrinogen (FBG) by an alveolar type II cell line stimulated with proinflammatory mediators and also in the inflamed pulmonary epithelium of animals with Pneumocystis carinii pneumonia suggest that extrahepatic FBG participates in the local acute phase response (APR) to infection and subsequent wound repair. However, the mechanisms that regulate extrahepatic FBG expression are poorly understood. This study compares the regulation of hepatic and pulmonary FBG expression by mediators of the APR, interleukin (IL)-6, IL-1beta, and dexamethasone (DEX), a synthetic glucocorticoid. Northern blotting and metabolic labeling studies revealed that IL-6 with or without DEX upregulates gammaFBG messenger RNA and protein, whereas IL-1beta inhibits gammaFBG expression in human lung (A549) and liver (HepG2) epithelial cells. In contrast, the addition of DEX relieved the IL-1beta-mediated inhibition of FBG expression in lung epithelial cells only; this response is termed "DEX rescue." Studies with cycloheximide indicate that only DEX rescue required de novo protein synthesis. Nuclear run-on analysis revealed no increase in gammaFBG transcription by DEX treatment. Although DEX treatment alone increased the stability of gammaFBG transcripts in lung cells, this effect was not observed in the presence of IL-1beta. Together, these results suggest that pre-existing transcription factors mediate the effects of IL-6 with or without DEX, DEX, and IL-1beta on gammaFBG gene expression in lung and liver cells. Also, the data suggest that DEX induces new protein synthesis of an inhibitor of IL-1beta signal transduction to effectively "rescue" FBG production in lung but not liver epithelial cells. This cell type-specific stimulation of FBG production by glucocorticoids to overcome IL-1beta inhibition may promote pulmonary wound repair mechanisms.

Immune-mediated inflammation directly impairs pulmonary function, contributing to the pathogenesis of Pneumocystis carinii pneumonia

The clinical severity of Pneumocystis carinii pneumonia (PCP) correlates closely with the appearance of pulmonary markers of inflammation. Therefore, a model system was developed whereby physiological studies could be performed on live mice to determine the extent to which pulmonary inflammation contributes to respiratory impairment during PCP. P. carinii-infected severe combined immunodeficient mice displayed little evidence of pulmonary inflammation and exhibited normal oxygenation and dynamic lung compliance. When comparably infected littermates were immunologically reconstituted, however, an intense immune-mediated inflammatory response was observed that resulted in significant decreases in both lung compliance and oxygenation. As the pneumonia resolved pulmonary function returned toward normal. To begin to define the cell populations contributing to inflammation-associated respiratory impairment during PCP, similar studies were performed in CD4(+) T cell-depleted mice. Mice depleted of both CD4(+) and CD8(+) cells developed infection, but they demonstrated neither abnormal lung compliance nor increased respiratory rate and displayed no markers of lung injury. In contrast, mice depleted of only CD4(+) T cells exhibited severe pulmonary inflammation and injury, decreased oxygenation and lung compliance, and increased respirations. Respiratory compromise was associated with the presence of activated CD8(+) cells and neutrophils in broncho-alveolar lavage fluid. These observations provide direct experimental evidence that the host's response to P. carinii directly impairs pulmonary function and contributes to the pathogenesis of PCP. Furthermore, CD8(+) T cells likely contribute to the respiratory compromise observed during PCP.

Chemokine gene expression during Pneumocystis carinii-driven pulmonary inflammation

Severe combined immunodeficient (SCID) mice lack functional lymphocytes and therefore develop Pneumocystis carinii pneumonia. However, when infected SCID mice are immunologically reconstituted with congenic spleen cells, a protective inflammatory cascade is initiated. Proinflammatory cytokines are produced, and lymphocytes and macrophages are recruited specifically to alveolar sites of infection. Importantly, uninfected regions of the lung remain free from inflammatory involvement, suggesting that there are specific mechanisms that limit inflammation in the infected lung. Therefore, to determine whether chemokines are involved in targeting the P. carinii-driven inflammatory response, steady-state mRNA levels of several chemokines were measured in the lungs of both reconstituted and nonreconstituted P. carinii-infected SCID mice. Despite significant organism burdens in the lungs of 8- and 10-week-old SCID mice, there was no evidence of elevated chemokine gene expression, which is consistent with the lack of an inflammatory response in these animals. However, when 8-week-old infected SCID mice were immunologically reconstituted, signs of focal pulmonary inflammation were observed, and levels of RANTES, MCP-1, lymphotactin, MIP-1alpha, MIP-1beta, and MIP-2 mRNAs were all significantly elevated. Chemokine mRNA abundance was elevated at day 10 postreconstitution (PR), was maximal at day 12 PR, and returned to baseline by day 22 PR. In situ hybridization demonstrated that during the peak of inflammation, RANTES gene expression was localized to sites of inflammatory cell infiltration and P. carinii infection. Thus, these observations indicate that chemokines play a role in the focal targeting of inflammatory cell recruitment to sites of P. carinii infection after the passive transfer of lymphocytes to the host.

Gamma interferon stimulates rat alveolar macrophages to kill Pneumocystis carinii by L-arginine- and tumor necrosis factor-dependent mechanisms

Pneumocystis carinii pneumonia remains a serious complication for immunocompromised patients. In the present study, P. carinii organisms interacted with gamma interferon (IFN-gamma)-stimulated alveolar macrophages (AMs) to activate the L-arginine-dependent cytocidal pathway involving reactive nitrogen intermediates (RNI) that were assayed as nitrite (NO2-). Unstimulated cultures of AMs produced negligible quantities of RNI. Addition of P. carinii organisms to IFN-gamma-primed AMs resulted in greatly enhanced production of RNI. NO2- levels increased from 0.8 +/- 0.4 to 11.1 +/- 3.8 microM as early as 6 h after P. carinii organisms were incubated with IFN-gamma-stimulated AMs and to 35.1 +/- 8.9 microM after a 24-h incubation, a near-maximum level. High levels of NO2- were produced by AMs primed with as little as 10 U of IFN-gamma per ml in the presence of P. carinii, and a 20-fold increase in IFN-gamma concentration resulted in only a further 65% increase in NO2- production. RNI-dependent killing of P. carinii was demonstrated by both a 51Cr release assay and a [35S]methionine pulse immunoprecipitation assay. Addition of either monoclonal tumor necrosis factor alpha (TNF-alpha) neutralizing antibody or 200 microM NG-monomethyl-L-arginine (L-NGMMA), a competitive inhibitor of the L-arginine-dependent pathway, significantly decreased NO2- production and reduced P. carinii killing. TNF-alpha alone had no effect on P. carinii viability. These results suggest that (i) the specific interaction of P. carinii organisms with IFN-gamma-primed AMs triggers the production of RNI, (ii) RNI are toxic to P. carinii, and (iii) TNF-alpha likely plays a central role in mediating P. carinii killing by IFN-gamma-stimulated AMs.

Induction of fibrinogen expression in the lung epithelium during Pneumocystis carinii pneumonia

Pneumocystis carinii is an important pulmonary pathogen responsible for morbidity and mortality in patients with AIDS. The acute-phase response (APR), the primary mechanism used by the body to restore homeostasis following infection, is characterized by increased levels of circulating fibrinogen (FBG). Although the liver is the primary site of increased FBG synthesis during the APR, we unexpectedly discovered that FBG is synthesized and secreted by lung alveolar epithelial cells in vitro during an inflammatory stimulus. Therefore, we sought to determine whether lung epithelial cells produce FBG in vivo using animal models of P. carinii pneumonia (PCP). Inflammation was noted by an influx of macrophages to P. carinii-infected alveoli. Northern hybridization revealed that gamma-FBG mRNA increased two- to fivefold in P. carinii-infected lung tissue, while RNA in situ hybridization demonstrated increased levels of gamma-FBG mRNA in the lung epithelium. Immunoelectron microscopy detected lung epithelial cell-specific production of FBG, suggesting induction of a localized inflammatory response resembling the APR. A systemic APR was confirmed by a two- to fivefold upregulation of the levels of hepatic gamma-FBG mRNA in animals with PCP, resulting in a corresponding increase in levels of FBG in plasma. Furthermore, immunoelectron microscopy revealed the presence of FBG at the junction of cell membranes of trophic forms of P. carinii organisms aggregated along the alveolar epithelium. These results implicate FBG in the pathogenesis of PCP in a manner similar to that of the adhesive glycoproteins fibronectin and vitronectin, which are known to participate in intra-alveolar aggregation of organisms and adherence of P. carinii to the lung epithelium.

Alterations in the expression of chemokine mRNA levels in fibrosis-resistant and -sensitive mice after thoracic irradiation

Fibrosis, characterized by the accumulation of collagen, is a consequence of a chronic inflammatory response. The purpose of this study was to determine if the mRNA expression of the chemokines, lymphotactin (Ltn), RANTES, eotaxin, macrophage inflammatory protein (MIP)-1 alpha, -1 beta, and -2, interferon-inducible protein 10 (IP-10), and monocyte chemotactic protein-1 (MCP-1), are altered during the development of radiation-induced pneumonitis and fibrosis. Further, we wished to determine if these changes differ between two strains of mice that vary in their sensitivity to radiation fibrosis. Fibrosis-sensitive (C57BL/6) and fibrosis-resistant (C3H/HeJ) mice were irradiated with a single dose of 12.5 Gy to the thorax. Total lung RNA was prepared and hybridized utilizing RNase protection assays. Data were quantified by phosphorimaging and results normalized to a constituitively expressed mRNA L32. 8 weeks post-irradiation most chemokines measured were elevated to varying degrees. The degree of elevation of each chemokine was identical in both strains. This suggested that chemotactic activity for neutrophils, macrophages, and lymphocytes were occurring during pneumonitis. By 26 weeks post-irradiation, messages encoding Ltn, RANTES, IP-10, and MCP-1 were elevated only in fibrosis sensitive (C57BL/6) mice. In situ hybridization demonstrated that MCP-1 and RANTES transcripts were produced predominantly from macrophages and lymphocytes. These studies suggest that lymphocytic recruitment and activation are key components of radiation-induced fibrosis.