Primary infection by Pneumocystis induces Notch-independent Clara cell mucin production in rat distal airways

Clara cells are the main airway secretory cells able to regenerate epithelium in the distal airways through transdifferentiating into goblet cells, a process under negative regulation of the Notch pathway. Pneumocystis is a highly prevalent fungus in humans occurring between 2 and 5 months of age, a period when airways are still developing and respiratory morbidity typically increases. Pneumocystis induces mucus hyperproduction in immunocompetent host airways and whether it can stimulate Clara cells is unknown. Markers of Clara cell secretion and Notch1 activation were investigated in lungs of immunocompetent rats at 40, 60, and 80 days of age during Pneumocystis primary infection with and without Valproic acid (VPA), a Notch inducer. The proportion of rats expressing mucin increased in Pneumocystis-infected rats respect to controls at 60 and 80 days of age. Frequency of distal airways Clara cells was maintained while mRNA levels for the mucin-encoding genes Muc5B and Muc5ac in lung homogenates increased 1.9 and 3.9 times at 60 days of infection (P. = 0.1609 and P. = 0.0001, respectively) and protein levels of the Clara cell marker CC10 decreased in the Pneumocystis-infected rats at 60 and 80 days of age (P. = 0.0118 & P. = 0.0388). CC10 and Muc5b co-localized in distal airway epithelium of Pneumocystis-infected rats at day 60. Co-localization of Muc5b and Ki67 as marker of mitosis in distal airways was not observed suggesting that Muc5b production by Clara cells was independent of mitosis. Notch levels remained similar and no transnucleation of activated Notch associated to Pneumocystis infection was detected. Unexpectedly, mucus was greatly increased at day 80 in Pneumocystis-infected rats receiving VPA suggesting that a Notch-independent mechanism was triggered. Overall, data suggests a Clara to goblet cell transdifferentiation mechanism induced by Pneumocystis and independent of Notch.

Pneumocystis elicits a STAT6-dependent, strain-specific innate immune response and airway hyperresponsiveness

It is widely held that exposure to pathogens such as fungi can be an agent of comorbidity, such as exacerbation of asthma or chronic obstructive pulmonary disease. Although many studies have examined allergic responses to fungi and their effects on pulmonary function, the possible pathologic implications of the early innate responses to fungal pathogens have not been explored. We examined early responses to the atypical fungus Pneumocystis in two common strains of mice in terms of overall immunological response and related pathology, such as cell damage and airway hyperresponsiveness (AHR). We found a strong strain-specific response in BALB/c mice that included recruitment of neutrophils, NK, NKT, and CD4 T cells. This response was accompanied by elevated indicators of lung damage (bronchoalveolar lavage fluid albumin and LDH) and profound AHR. This early response was absent in C57BL/6 mice, although both strains exhibited a later response associated with the clearance of Pneumocystis. We found that this AHR could not be attributed exclusively to the presence of recruited neutrophils, NKT, NK, or CD4 cells or to the actions of IFN-γ or IL-4. However, in the absence of STAT6 signaling, AHR and inflammatory cell recruitment were virtually absent. Gene expression analysis indicated that this early response included activation of several transcription factors that could be involved in pulmonary remodeling. These results show that exposure to a fungus such as Pneumocystis can elicit pulmonary responses that may contribute to morbidity, even without prior sensitization, in the context of certain genetic backgrounds.

[Effects of Fructus Psoralea and Brucea javanica on the level of IL-2 and NK cell in rats infected with Pneumocystis carinii]

SD rat model of PCP was established by subcutaneous injection with dexamethasone. The treatment groups received Fructus Psoralea (FP, 10.0 mg/kg), Brucea javanica (BJ, 1.2 mg/kg) and a mixture of the two Chinese herbs(FP 5mg/kg, BJ 0.6 mg/kg) respectively. By means of detecting the level of IL-2 in sera and NK cells in spleens, the effect of FP and BJ on the level of IL-2 and NK cells in rats with Pneumocystis carinii pneumonia (PCP) was observed, with SMZco treatment group (TMP 50 mg/kg, SMZ 250 mg/kg) and groups of infected and normal rats as controls. Compared with the infected group, the level of IL-2(526.1 +/- 5.5) pg/ml and NK cells (27.1% +/- 0.8%) significantly increased in the FP group (P < 0.01), followed by the FP/BJ combination group [(314.7 +/- 6.7) pg/ml, 22.9% +/- 0.9%) (P < 0.05)], and BJ group [(285.4 +/- 6.1) pg/ml, 20.7% +/- l.0%) (P < 0.05)]. Chinese herbs Fructus Psoralea and Brucea javanica show an immune regulatory action on the PCP rats.

[Enzyme change in bronchoalveolar lavage fluid of pneumocystis pneumonia rats and the effect of garlicin treatment]

OBJECTIVE

To study the change of enzymes and effect of garlicin treatment on the change in bronchoalveolar lavage fluid (BALF) of rats with Pneumocystis carinii pneumonia (PCP).

METHODS

Wistar rats were injected intramuscularly continually with dexamethasone to establish the rat model of PCP. The experimental rats (group A) were injected intramuscularly with garlicin at a dose of 10 mg/(kg x d) for 5 days in the 3rd, 6th and 9th week respectively, and SMZ/TMP therapy group (B), PCP infected group (C) and normal group (D) were established as controls. Three days after the last treatment, the rats of all groups were killed and BALF was collected without contamination and enzymes AST, ALF, CHE, ALP, LDH, CK, CKMB, HBDH, AFU, 5'NT, ADA were examined.

RESULTS

The ALP level in group C [(573.41 +/- 350.63)U/L] was significantly higher than that in group D [(210.56 +/- 114.41) U/L] (q = 4.682, P < 0.01), group A [(392.07 +/- 217.57) U/L] (q = 3.851, P < 0.05), and group B [(325.21 +/- 180.65) U/L] (q = 4.380, P < 0.01); the level of CK, CKMB and 5'NT in group C [948.94 +/- 403.43, 489.47 +/- 254.46 and (6.76 +/- 3.11) U/L respectively] was higher than those in group D [426.22 +/- 319.00, 213.33 +/- 144.54 and (3.22 +/- 1.20) U/L] (q = 4.696, 3.784, 3.812, P< 0.05); there was no significant difference in the level of AST, ALT, CHE, LDH, HBDH, AFU and ADA among the four groups (F = 1.852, 0.958, 2.470, 1.423, 1.178, 1.342, 0.611, P > 0.05).

CONCLUSIONS

The level of ALP, CK, CKMB but the ALP level decreases distinctly after the garlicin and 5'NT increases evidently in BALF of PCP infected rats, but the ALP level decreases distinctly after the garlicin treatment.

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.

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.

Enhanced lung injury and delayed clearance of Pneumocystis carinii in surfactant protein A-deficient mice: attenuation of cytokine responses and reactive oxygen-nitrogen species

Surfactant protein A (SP-A), a member of the collectin family, selectively binds to Pneumocystis carinii and mediates interactions between pathogen and host alveolar macrophages in vitro. To test the hypothesis that mice lacking SP-A have delayed clearance of Pneumocystis organisms and enhanced lung injury, wild-type C57BL/6 (WT) and SP-A-deficient mice (SP-A(-/-)) with or without selective CD4(+)-T-cell depletion were intratracheally inoculated with Pneumocystis organisms. Four weeks later, CD4-depleted SP-A-deficient mice had developed a more severe Pneumocystis infection than CD4-depleted WT (P. carinii pneumonia [PCP] scores of 3 versus 2, respectively). Whereas all non-CD4-depleted WT mice were free of PCP, intact SP-A(-/-) mice also had evidence of increased organism burden. Pneumocystis infection in SP-A-deficient mice was associated histologically with enhanced peribronchial and/or perivascular cellularity (score of 4 versus 2, SP-A(-/-) versus C57BL/6 mice, respectively) and a corresponding increase in bronchoalveolar lavage (BAL) cell counts. Increases in SP-D content, gamma interferon, interleukin-4, interleukin-5, and tumor necrosis factor alpha in BAL fluid occurred but were attenuated in PCP-infected SP-A(-/-) mice compared to WT mice. There were increases in total BAL NO levels in both infected groups, but nitrite levels were higher in SP-A(-/-) mice, indicating a reduction in production of higher oxides of nitrogen that was also reflected in lower levels of 3-nitrotyrosine staining in the SP-A(-/-) group. We conclude that despite increases in inflammatory cells, SP-A-deficient mice infected with P. carinii exhibit an enhanced susceptibility to the organism and attenuated production of proinflammatory cytokines and reactive oxygen-nitrogen species. These data support the concept that SP-A is a local effector molecule in the lung host defense against P. carinii in vivo.

Alteration in expression of the rat mitochondrial ATPase 6 gene during Pneumocystis carinii infection

BACKGROUND

Pneumocystis carinii causes pneumonia in immunocompromised patients with a high morbidity and mortality rate, but the interaction between this organism and the host cell is not well understood. The purpose of this research was to study the response of host cells to P. carinii infection on a molecular level.

RESULTS

The technique of mRNA differential display was used to detect genes whose expression may be affected by P. carinii infection. The nucleotide sequence of one differentially displayed DNA fragment was found to be identical to that of the rat mitochondrial ATPase 6 gene, which is a subunit of the F0F1-ATP synthase complex. A four-fold increase in expression of this gene was verified by Northern blot analysis of total RNA extracted from P. carinii-infected rat lung versus that from mock-infected rat lung. Localization of the cells containing ATPase 6 mRNA was accomplished by in situ hybridization. In sections of non-infected rat lung, these cells were found lining the distal parts of the respiratory tree and in apical areas of the alveoli. Histological location of these cells suggested that they were Clara cells and type II pneumocytes. This hypothesis was confirmed by co-localizing the mRNAs for ATPase 6 and surfactant protein B (SP-B) to the same cells by two-color fluorescent in situ hybridization.

CONCLUSIONS

The ATPase 6 gene is over expressed during P. carinii infection, and type II pneumocytes and Clara cells are the cell types responsible for this over-expression.

The impact of CMV on the respiratory burst of macrophages in response to Pneumocystis carinii

Infection of human monocyte-derived macrophages with CMV decreased the respiratory burst when cells were stimulated with opsonized zymosan or Pneumocystis carinii (P. carinii). Such an effect, though smaller, was also seen with heat-inactivated CMV, but only when triggered by zymosan. The effect was most pronounced in cells obtained from CMV antibody-negative donors. Dexamethasone further reduced the respiratory burst, both in uninfected and CMV-infected cells. Interferon-gamma increased the response in uninfected cells and, to a lesser extend, in cells treated with heat-inactivated CMV, whereas no effect was seen with infective CMV. No overt productive infection or cytopathology could be detected, however, the monocytes incubated with infective but also heat-inactivated CMV formed clusters, a phenomenon that was equally pronounced in cultures from CMV antibody positive and negative-donors. These results might help explain the worse prognosis of P. carinii pneumonia in patients coinfected with CMV and receiving dexamethasone.

Pneumocystis carinii pneumonia in HIV-infected patients: effect of steroid therapy on surfactant level

Previous studies have suggested alterations in pulmonary surfactant lipid in the setting of Pneumocystis carinii pneumonia in HIV-infected patients. Because pulmonary surfactant lipid is composed of a variety of lipid products and because other phospholipids might be present in bronchoalveolar lavage (BAL) lipid determinations, a single molecular species of phospholipid which comprises a substantial portion of the surfactant lipid fraction, dipalmitoyl phosphatidylcholine (DPPC), was measured by capillary column gas chromatography in BAL samples taken at the time of the diagnosis of P. carinii pneumonia, and 10 days after treatment for P. carinii pneumonia. DPPC was measured at day 0 and day 10 in seven patients who had been randomized to receive methylprednisolone adjuvant therapy for P. carinii pneumonia and in six patients who had been randomized to not receive methylprednisolone therapy. The level of DPPC in BAL from all patients at day 0 was 0.49 +/- 0.06 microgram ml-1 BAL. This level is significantly lower that the level of DPPC determined in BAL from five normal volunteers 2.48 +/- 0.40 micrograms ml-1. At day 0, the BAL level of DPPC in patients treated with methylprednisolone was not different from the BAL level of DPPC in patients not treated with methylprednisolone. By day 10 of therapy for P. carinii pneumonia, BAL levels of DPPC in all patients had increased to 1.05 +/- 0.19 micrograms ml-1 BAL. At day 10 DPPC levels in the methylprednisolone treated group were not different from the group not treated with methylprednisolone. We conclude that in HIV-infected patients, lung surfactant lipid is reduced in the setting of P. carinii pneumonia. The lipid levels return toward normal levels with treatment. Adjuvant therapy with corticosteroids does not alter the rate of recovery of surfactant lipid levels at least after 10 days of therapy.

Pneumocystis carinii glycoprotein A inhibits surfactant phospholipid secretion by rat alveolar type II cells

Pneumocystis carinii pneumonia (PCP) remains a major cause of morbidity in AIDS. The pathogenesis of PCP is poorly understood, but evidence of surfactant abnormalities is mounting. The role of the major surface glycoprotein of P. carinii, gpA, in producing surfactant abnormalities was investigated. Rat type II pneumocytes were incubated with [3H]choline, purified gpA, and modulators. Lipid was extracted, and [3H]dipalmitoyl phosphatidylcholine (DPPC) secretion was calculated. Contaminating endotoxin had no effect on DPPC secretion. gpA inhibited basal and ATP-stimulated DPPC secretion in a dose- and time-dependent manner. An anti-gpA monoclonal antibody attenuated inhibition of DPPC secretion. Unglycosylated recombinant gpA inhibited secretion, suggesting that functional activity resides in the protein moiety of gpA. These results suggest that gpA is a specific trigger for abnormalities of surfactant lipids in PCP. This is a unique role for a microbial product in disease pathogenesis and a potentially exploitable therapeutic target.

Expression of the alpha 5 beta 1 fibronectin receptor on T lymphocytes of patients with HIV-1 infection

AIMS

To evaluate the expression of the alpha 5 beta 1 integrin fibronectin receptor (FNR), which mediates several processes, including phagocytosis, cell motility and the immune response, on T lymphocytes of patients with HIV-1 infection.

METHODS

T lymphocytes were incubated with monoclonal antibody directed against FNR and then with monoclonal antibodies, conjugated with phycoerythrin, directed against CD3, CD4 and CD8 positive cells. Expression of FNR on CD3, CD4 and CD8 positive cells was analysed using flow cytometry.

RESULTS

Normal expression of FNR was observed on CD3 positive cells from asymptomatic HIV positive patients and those with AIDS. Increased expression of FNR was observed on CD8 positive cells from asymptomatic HIV positive patients and on CD4 positive cells from patients with AIDS. Increased FNR expression was observed on CD4 positive cells from patients with AIDS, particularly those with opportunistic infections caused by Pneumocystis carinii, Mycobacterium sp, Toxoplasma gondii, and Cryptococcus neoformans.

CONCLUSION

Increased expression of FNR on CD8 and CD4 positive cells in asymptomatic HIV positive patients and those with AIDS, respectively, may be an epiphenomenon correlated with lymphocyte activation by HIV-1 or opportunistic infection, Further study is required to determine whether upregulation of FNR expression has a direct role in the pathogenesis of AIDS.