Anti-inflammatory effects of PDMP in Pneumocystis pneumonia (133.1)

Glycosphingolipid (GSL) Lactosyl Ceramide (LacCer) is thought to be involved in Pneumocystis interaction with the host. Our previous results show that treatment with glycosphingolipid synthesis inhibitor PDMP reduces the fungus lung burden as well as symptoms of inflammation in mice with Pneumocystis pneumonia (PCP). Experiments were set up to resolve whether anti-inflammatory effects were due to the specific mechanisms involved in innate immune responses to Pneumocystis, or to some general anti-inflammatory property of PDMP. Animals were infected with live organisms, or challenged with either beta-glucan (the pro-inflammatory component of Pneumocystis cell wall) or LPS (inducer of lung inflammation unrelated to Pneumocystis). At the experimental endpoint the following inflammatory parameters were assessed: leukocyte recruitment to the lungs, production of pro-inflammatory cytokines and chemokines, histopathology and lung damage. Results show that glucan-induced acute inflammation partially mimics the inflammation caused by the whole organism, and PDMP suppresses some of the inflammatory parameters affected in PCP. In contrast, although LPS induces comparable intensity of inflammation as live Pneumocystis or glucan, PDMP does not suppress any inflammatory parameters measured in this group. These results suggest that the mechanism of PDMP action is related to the features specific to Pneumocystis and host recognition of the microorganism. Further studies will attempt to determine the role of LacCer in these processes.

Supported by NIH-RO1-HL62150 and Mayo Clinic

Fitness of cell-mediated immunity independent of repertoire diversity

Fitness of cell-mediated immunity is thought to depend on TCR diversity; however, this concept has not been tested formally. We tested the concept using JH(-/-) mice that lack B cells and have TCR Vbeta diversity <1% that of wild-type mice and quasimonoclonal (QM) mice with oligoclonal B cells and TCR Vbeta diversity 7% that of wild-type mice. Despite having a TCR repertoire contracted >99% and defective lymphoid organogenesis, JH(-/-) mice rejected H-Y-incompatible skin grafts as rapidly as wild-type mice. JH(-/-) mice exhibited T cell priming by peptide and delayed-type hypersensitivity, although these responses were less than normal owing either to TCR repertoire contraction or defective lymphoid organogenesis. QM mice with TCR diversity contracted >90%, and normal lymphoid organs rejected H-Y incompatible skin grafts as rapidly as wild type mice and exhibited normal T cell priming and normal delayed-type hypersensitivity reactions. QM mice also resisted Pneumocystis murina like wild-type mice. Thus, cell-mediated immunity can function normally despite contractions of TCR diversity >90% and possibly >99%.

The role of LacCer inhibitor in modulation of established Pneumocystis pneumonia (91.1)

Pneumocystis pneumonia is caused, at least partly, by inflammatory action of β-glucan, the major component of Pneumocystis cell wall. Glucan induces release of pro-inflammatory cytokines in alveolar macrophages and lung epithelial cells. While macrophages recognize glucan mainly by dectin receptors, epithelial cells utilize membrane glycosphingolipid (GSL) lactosyl ceramide (LacCer) as glucan-binding molecule. The use of GSL inhibitors in vitro causes reduced NF-κB activation and inhibited IL-8 release in epithelial cells. To assess the impact of LacCer in lung inflammation, we treated Pneumocystis-infected mice with GSL inhibitor PDMP. The animals were immunosuppressed by GK 1.5 antibody, infected with Pneumocystis by intratracheal injection and, starting at 8 weeks post infection, treated with either 150 mg PDMP/kg of body weight - dissolved in saline, or equal volume of saline alone (daily i.p. injections for 10 days). The analysis of sacrificed animals showed that PDMP-treated mice had fewer leukocytes in the bronchoalveolar lavage fluid (BALF) than saline-treated controls with the most marked difference in the number of neutrophils. Interestingly, BALF concentrations of MIP-2 and TNF-α (determined by ELISA) did not differ between these two groups. The analysis of Pneumocystis burden in the lung, as determined by Q-PCR, showed a trend of decreased Pneumocystis-specific DNA copies in PDMP-treated animals. These results suggest that PDMP might have an impact on inflammatory response to Pneumocystis. Other GSL inhibitors are yet to be tested in similar in vivo experiments. This might lead to new options in treatment of Pneumocystis pneumonia.

Supported by NIH RO1 HL62150 and Mayo

Pneumocystis Cell Wall β-Glucans Induce Dendritic Cell Costimulatory Molecule Expression and Inflammatory Activation through a Fas-Fas Ligand Mechanism

Respiratory failure during Pneumocystis pneumonia is mainly a consequence of exaggerated inflammatory responses to the organism. Dendritic cells (DCs) are the most potent APCs in the lung and are key to the regulation of innate and adaptive immune responses. However, their participation in the inflammatory response directed against Pneumocystis infection has not been fully elucidated. Therefore, we studied the role of Pneumocystis carinii, as well as Saccharomyces cerevisiae, cell wall-derived beta-glucans, in DC costimulatory molecule expression. We further studied the impact of beta-glucans on subsequent T cell activation. Because cytokine secretion by DCs has recently been shown to be regulated by Fas ligand (FasL), its role in beta-glucan activation of DCs was also investigated. beta-Glucan-induced DC activation occurred in part through dectin-1 receptors. We demonstrated that DC activation by beta-glucans elicits T cell activation and polarization into a Th1 patterned response, but with the conspicuous absence of IL-12. These observations differed from LPS-driven T cell polarization, suggesting that beta-glucans and LPS signal DC activation through different mechanisms. We additionally determined that IL-1beta and TNF-alpha secretion by beta-glucan-stimulated DCs was partially regulated by Fas-FasL. This suggests that dysregulation of FasL could further enhance exuberant and prolonged cytokine production by DCs following DC-T cell interactions, further promoting lung inflammation typical of Pneumocystis pneumonia.

Surfactant protein D enhances Pneumocystis infection in immune-suppressed mice

To further determine the role of surfactant protein (SP)-D in the pathogenesis of Pneumocystis pneumonia, a mouse model of transgenic overexpression (OE) of SP-D was studied. These animals produce roughly 30- to 50-fold greater SP-D than their wild-type (WT) counterparts but show no other differences in lung morphology and function. Animals in both the SP-D OE and WT groups were depleted of CD4 lymphocytes with weekly injections of GK1.5 antibody, before Pneumocystis inoculation, and throughout the subsequent infection period. At various time points, mice were killed and analyzed for inflammatory parameters and organism burden. Proinflammatory cytokines in bronchoalveolar lavage fluid were elevated throughout the period of infection, with OE animals exhibiting significantly higher levels of TNF-alpha and macrophage inflammatory protein-2 compared with WT controls. The total number of cells in the lavage fluid was also increased significantly only in the OE group, whereas the cell differential composition demonstrated lymphocyte and eosinophil infiltration in both groups of animals. Significantly, the organism burden was markedly higher in the SP-D OE animals, whereas the WT mice demonstrated little alteration in organism number over the course of infection. These results further indicate that SP-D facilitates the development of Pneumocystis infection and related lung inflammation in an immunosuppressed mouse model.

Increased CD4+ T cell infiltrates in rheumatoid arthritis-associated interstitial pneumonitis compared with idiopathic interstitial pneumonitis

OBJECTIVE

To study lymphocyte markers in rheumatoid arthritis (RA)-associated interstitial pneumonitis (IP) compared with idiopathic IP.

METHODS

Paraffin-embedded lung biopsy specimens from patients with RA (n = 15) and from those without RA (n = 16), all of whom had a diagnosis of either nonspecific IP or usual IP, were studied. Tissue sections from each patient were reviewed by a pathologist, who was blinded to the clinical data. Age and pulmonary function test results were similar in RA and non-RA patients. After high-temperature antigen unmasking, sections were incubated with mouse monoclonal antibodies directed against CD3, CD4, CD8, CD16, and CD20. All slides were coded, and digital images (100x magnification) of the entire tissue area were obtained. Staining was quantified using computer-assisted image analysis.

RESULTS

Staining for CD4 was more prominent in patients with RA than in the non-RA comparison group (median 9.3 cells/mm(2), interquartile range [IQR] 5.5-27.3 versus 0.6 cells/mm(2), IQR 0.2-1.9; P = 0.002). CD4+ cell counts were increased in RA patients with nonspecific IP as well as in RA patients with usual IP, with no major difference between these groups. Results were similar for quantification of CD3 (P = 0.012). There was a less striking trend toward more CD8+ cells in RA patients (P = 0.27 versus those with non-RA lung disease).

CONCLUSION

IP lesions in patients with RA are characterized by an increased number of CD4+ cells, as compared with that in patients with idiopathic IP. This finding suggests that CD4+ T cells are critical for the development of pulmonary manifestations in RA, and may have implications for the treatment of RA-associated lung disease.

Etanercept for the treatment of stage II and III progressive pulmonary sarcoidosis

BACKGROUND

Tumor necrosis factor (TNF)-alpha is produced by macrophages and other cells, and is believed to participate in granulomatous inflammation. Targeted antagonism of TNF-alpha has been proposed as a novel treatment strategy for sarcoidosis. Etanercept is a dimeric fusion protein that binds specifically to TNF-alpha, rendering it biologically inactive.

OBJECTIVE

To assess whether etanercept has potential efficacy in the treatment of progressive pulmonary sarcoidosis.

DESIGN

Prospective, open-label, phase-2 treatment trial.

SETTING

Mayo Clinic, Rochester, MN.

PATIENTS

Stage II or III progressive pulmonary sarcoidosis.

INTERVENTION

Etanercept, 25 mg subcutaneously twice weekly.

MEASUREMENTS

Pulmonary function, chest radiographs, dyspnea, and TNF-alpha levels in serum and BAL fluid.

RESULTS

The study was terminated after the enrollment of 17 patients due to an early-stop clause of the pretrial study design related to excessive treatment failures. Neither absolute levels of TNF-alpha nor TNF-alpha activity in the serum, BAL fluid, or alveolar macrophages were able to predict which patients would respond to etanercept.

CONCLUSIONS

In patients with progressive stage II or III pulmonary sarcoidosis, etanercept was frequently associated with early or late treatment failure. These data would not support the design of a large multicenter randomized trial comparing etanercept with conventional corticosteroid therapy.

Surfactant protein D-mediated aggregation of Pneumocystis carinii impairs phagocytosis by alveolar macrophages

Pneumocystis carinii remains an important and potentially fatal cause of opportunistic pneumonia. Animal studies reveal that substantial quantities of surfactant protein D (SP-D) accumulate in the airspaces during P. carinii pneumonia and are particularly abundant in aggregates of organisms. Due to the multimeric structure of SP-D, we hypothesized that SP-D mediates aggregation of the organism. From previous clinical studies it is known that aggregated organisms are conspicuous in sections of lung tissue and bronchoalveolar lavage (BAL) fluids of humans with active P. carinii pneumonia. Herein, we observe that SP-D levels increased at least fourfold in BAL fluids of patients with P. carinii pneumonia. Next, a spectrophotometric sedimentation assay was developed to assess the aggregation of P. carinii in vitro by SP-D. P. carinii organisms were first stripped with glutathione to remove bound SP-D and subsequently incubated in the presence of SP-D and 2 mM calcium. P. carinii incubated with natural SP-D (10 micro g/ml) containing dodecamers and higher-order forms exhibited aggregation and enhanced sedimentation compared to that of glutathione-stripped P. carinii. Aggregation was also enhanced by the concentrated supernatant of rat BAL fluid, and this effect was abolished by the selective removal of SP-D from the lavage fluid. P. carinii aggregation was reduced by maltose, mannose, and EDTA, consistent with the role of the SP-D C-type lectin domain (CRD) in the aggregation event. Comparisons of different molecular forms of SP-D showed that dodecamers-but not trimeric subunits-mediate optimal aggregation of P. carinii. Aggregation of P. carinii by SP-D was shown to be responsible for the impaired phagocytosis of the organisms by alveolar macrophages. Thus, SP-D-mediated aggregation of P. carinii may represent one means by which the organism avoids elimination by the host.

Removal of bronchoalveolar cells augments the late eosinophilic response to segmental allergen challenge

BACKGROUND

In patients with quiescent asthma, macrophages are the most prevalent cells recovered by bronchoalveolar lavage (BAL). Through activation via their FcepsilonRII receptors or by acting as antigen-presenting cells, macrophages could, in theory, promote the late airway response to allergen.

OBJECTIVE

In order to investigate the importance of macrophages and other airway luminal cells in inducing the late airway response, a novel washout experiment was designed.

METHODS

Five patients with ragweed-allergic asthma underwent bronchoscopy and segmental bronchial challenge with either normal saline or short ragweed extract in two segments of one lung. In a third segment of the opposite lung, 12 successive BALs (25 mL each) were performed, followed by challenge with an identical dose of short ragweed (washed-challenged segment). After 24 h, all three challenged segments underwent BAL.

RESULTS

Initially, in the washed-challenged segment, over 80% (mean 80.4%, range 68-88%) of the recoverable airway dwelling cells were removed. Unexpectedly, 24 h later these same washed-challenged segments contained more eosinophils in the BAL than the challenged segments from the opposite lung (P = 0.033).

CONCLUSIONS

Removing the majority of airway luminal cells followed by allergen bronchoprovocation increased the number of eosinophils recovered 24 h after challenge. Our results suggest that in quiescent allergic asthma, the airway luminal cells are protective and attenuate the late eosinophilic response to allergen challenge.

Carbohydrate recognition domain of surfactant protein D mediates interactions with Pneumocystis carinii glycoprotein A

Pneumocystis carinii continues to cause severe pneumonia in immunocompromised patients. Surfactant protein D (SP-D), a lung collectin, markedly accumulates during P. carinii pneumonia and binds to glycoprotein A (gpA) on the surface of P. carinii, thereby enhancing interactions with alveolar macrophages. Herein, we report the structural basis of the interaction of SP-D with gpA. We demonstrate that natural SP-D binds to purified gpA in the presence of 2 mM calcium in a saturable, concentration-dependent manner, which is abolished by 10 mM ethylenediaminetetraacetic acid. Increasing concentrations of calcium under otherwise cation-free conditions significantly enhance SP-D binding to gpA, whereas manganese and magnesium cations have minimal effect. Maximal SP-D binding occurs at pH 7.4, with significant inhibition at pH 4. SP-D binding to gpA is also competitively inhibited by maltose>glucose>mannose>N-acetyl-glucosamine. Comparison of the binding of various natural and recombinant forms of SP-D to gpA reveals that the number of carbohydrate recognition domains (CRDs) in a given SP-D form determines the relative extent of binding to gpA. Maximal binding is observed with natural SP-D (dodecamers and higher order SP-D complexes) followed by recombinant dodecamers. In contrast, recombinant full-length trimers exhibit substantially less binding, which is similar to that observed with a recombinant truncated molecule consisting of the CRD and neck regions, and containing trimers of this portion of the molecule. Taken together, these findings strongly indicate that the CRD of SP-D mediates interaction with P. carinii gpA through its attached oligosaccharides and that the extent of SP-D binding to P. carinii is greatest with dodecamers and higher order forms of SP-D.

Mechanisms of defence in the lung: lessons from Pneumocystis carinii pneumonia

Pneumocystis carinii continues to represent an important complication of individuals with compromised immunity. P. carinii interacts with immune and non-immune cells in the lung and mediates lung injury through a variety of mechanisms. CD4+ T lymphocytes are the cornerstone in defence against P. carinii. Recent studies indicate that alveolar macrophages provide essential functions that significantly enhance clearance of P. carinii infection. P. carinii also attaches to alveolar epithelial cells, causing inhibition of epithelial growth and replication. In addition to cellular interactions, P. carinii organisms bind to a variety of host adhesive proteins present in the lower respiratory tract. Binding of these proteins to P. carinii modulates host cell recognition and immune responses to the parasite. During the course of P. carinii pneumonia, several inflammatory mediators are produced in the lung. Although necessary for control of infection, exuberant inflammatory responses also predispose the host to the development of acute lung injury. Thus, host defences against P. carinii depend on complex interactions between immune and non-immune cells as well as several mediators that facilitate host recognition and eventual elimination of infection. Understanding these complex processes may enable development of novel therapeutic approaches for management of this important infection.