Analysis of cellular response and gamma interferon synthesis in bronchoalveolar lavage fluid and lung homogenate of mice infected with Pneumocystis carinii

Plasma IL-6/IL-10 Ratio and IL-8, LDH, and HBDH Level Predict the Severity and the Risk of Death in AIDS Patients with Pneumocystis Pneumonia

Objective. To identify blood biomarkers to predict severity and mortality in AIDS PCP patients. Methods. Biomarkers including clinical parameters and plasma inflammatory cytokines were assessed in 32 HIV-infected patients with Pneumocystis pneumonia (PCP) at time of admission. Predictive value of the biomarkers for clinical severity and in-hospital mortality was evaluated by corresponding ROC curve. Results. Levels of CRP, WBC, LDH, HBDH, and Ferritin were significantly higher in the severe and nonsurvivor AIDS PCP patients. These important biochemical indicators have inverse correlation with oxygenation index, especially levels of LDH (P = 0.008, R (2) = 0.258), HBDH (P = 0.001, R (2) = 0.335), and Ferritin (P = 0.005, R (2) = 0.237). Plasma IL-8 and IL-6 levels were significantly higher in patients with PaO2/FiO2 ≤ 200 mmHg and nonsurvivors than in those with PaO2/FiO2 > 200 mmHg and survivors. Severe and nonsurvival groups showed higher ratio of mean IL-6/IL-10 level (1.78 ± 1.56, P < 0.001; 1.11 ± 0.72, P = 0.043), larger AUC (95% CI 0.781-1.000, P < 0.001; 95% CI 0.592-0.917, P = 0.043), and more significantly inverse correlation with the oxygenation index. Conclusion. Plasma IL-8, LDH, and HBDH levels and IL-6/IL-10 ratio could be helpful for early evaluation of the severity and predicting fatal outcomes in AIDS PCP patients.

Pneumocystis Carinii Pneumonia in Adult Non-HIV Disorders

Pneumocystis carinii pneumonia (PCP) remains a serious infection in the immunocompromised host (in the absence of HIV infection) and presents significant management and diagnostic challenges to ICU physicians. Non-HIV PCP is generally abrupt in onset, and follows a fulminate course with high rates of hospitalization, ICT admission, respiratory failure, and requirement for intubation. Mortality is generally high, especially if mechanical ventilation is required. Non-invasive ventilatory support may be considered, although the rapid progression to respiratory failure often necessitates intubation at the time of presentation. Bronchoscopy is often required to establish the diagnosis, and empirical antimicrobial treatment specifically targeted to P. carinii should be initiated while awaiting confirmation. Adjunctive corticosteroids may accelerate recovery, although their use has not yet been established in non-HIV PCP. For the ICU physicians to diagnose PCP, the non-specific presentation of an acute febrile illness and respiratory distress with diffuse pulmonary infiltrates requires a high clinical index of suspician, familiarity with clinical conditions associated with increased risk for PCP, and a low threshold for bronchoscopy to establish the diagnosis.

Colonization by Pneumocystis jirovecii and its role in disease

Although the incidence of Pneumocystis pneumonia (PCP) has decreased since the introduction of combination antiretroviral therapy, it remains an important cause of disease in both HIV-infected and non-HIV-infected immunosuppressed populations. The epidemiology of PCP has shifted over the course of the HIV epidemic both from changes in HIV and PCP treatment and prevention and from changes in critical care medicine. Although less common in non-HIV-infected immunosuppressed patients, PCP is now more frequently seen due to the increasing numbers of organ transplants and development of novel immunotherapies. New diagnostic and treatment modalities are under investigation. The immune response is critical in preventing this disease but also results in lung damage, and future work may offer potential areas for vaccine development or immunomodulatory therapy. Colonization with Pneumocystis is an area of increasing clinical and research interest and may be important in development of lung diseases such as chronic obstructive pulmonary disease. In this review, we discuss current clinical and research topics in the study of Pneumocystis and highlight areas for future research.

Defective nitric oxide production by alveolar macrophages during Pneumocystis pneumonia

The effect of nitric oxide (NO) on Pneumocystis (Pc) organisms, the role of NO in the defense against infection with Pc, and the production of NO by alveolar macrophages (AMs) during Pneumocystis pneumonia (PCP) were investigated. The results indicate that NO was toxic to Pc organisms and inhibited their proliferation in culture. When the production of NO was inhibited by intraperitoneal injection of rats with the nitric oxide synthase inhibitor L-N(5)-(1-iminoethyl) ornithine, progression of Pc infection in immunocompetent rats was enhanced. Concentrations of NO in bronchoalveolar lavage fluids from immunosuppressed, Pc-infected rats and mice were greatly reduced, compared with those from uninfected animals, and AMs from these animals were defective in NO production. However, inducible nitric oxide synthase (iNOS) mRNA and protein concentrations were high in AMs from Pc-infected rats and mice. Immunoblot analysis showed that iNOS in AMs from Pc-infected rats existed primarily as a monomer, but the homo-dimerization of iNOS monomers was required for the production of NO. When iNOS dimerization cofactors, including calmodulin, were added to macrophage lysates, iNOS dimerization increased, whereas incubation of the same lysates with all cofactors except calmodulin did not rescue iNOS dimer formation. These data suggest that NO is important in the defense against Pc infection, but that the production of NO in AMs during PCP is defective because of the reduced dimerization of iNOS.

Current understanding of Pneumocystis immunology

Pneumocystis jirovecii is the opportunistic fungal organism that causes Pneumocystis pneumonia (PCP) in humans. Similar to other opportunistic pathogens, Pneumocystis causes disease in individuals who are immunocompromised, particularly those infected with HIV. PCP remains the most common opportunistic infection in patients with AIDS. Incidence has decreased greatly with the advent of HAART. However, an increase in the non-HIV immunocompromised population, noncompliance with current treatments, emergence of drug-resistant strains and rise in HIV(+) cases in developing countries makes Pneumocystis a pathogen of continued interest and a public health threat. A great deal of research interest has addressed therapeutic interventions to boost waning immunity in the host to prevent or treat PCP. This article focuses on research conducted during the previous 5 years regarding the host immune response to Pneumocystis, including innate, cell-mediated and humoral immunity, and associated immunotherapies tested against PCP.

Immunity against the opportunistic fungal pathogen Pneumocystis

Species of the genus Pneumocystis exist as opportunistic fungal pathogens and are associated with severe pneumonia and pulmonary complications in immunocompromised individuals. Although prophylactic therapy for Pneumocystis has significantly decreased the overall incidence of infection, more than 80% of cases in current patient populations are considered breakthrough cases. In the HIV-infected population, in the years following the initiation of highly active antiretroviral therapy (HAART), significant reductions in the incidence of Pneumocystis infection were observed, although trends over the last several years suggest that the incidence of Pneumocystis has plateaued rather than decreased. Furthermore, with the more prominent usage of immunosuppressive therapies, the frequency of Pneumocystis infection in the HIV-negative population, such as those with hematologic malignancies and those who have undergone transplantation, has risen significantly. Investigating host defense mechanisms against P. carinii has historically been problematic due to the difficulty in achieving continuous in vitro propagation of proliferating Pneumocytis organisms. Nevertheless, clinical and experimental studies have documented that host defense against Pneumocystis involves a concerted effort between innate, cell-mediated (T lymphocyte) and humoral (B lymphocyte) responses. However, the pulmonary environment is a tissue site where heightened inflammatory responses can often lead to inflammation-mediated injury, thereby contributing to the pathogenesis of Pneumocystis infection. Accordingly, clearance of Pneumocystis from the pulmonary environment is dependent on a delicate equilibrium between the inflammatory response and immune-mediated clearance of the organism. Furthermore, innate and adaptive responses against Pneumocystis are strikingly similar to those against other medically-important fungi, thus providing additional evidence that Pneumocystis exists as a fungal organism.

Pneumocystis jiroveci Pneumonia in Adult Patients with AIDS

Pneumocystis jiroveci (P. carinii) is an opportunistic pathogen that has gained particular prominence since the onset of the AIDS epidemic. Among several important advances in diagnosis and management, appropriately targeting chemoprophylaxis to HIV-infected patients at high clinical risk for P. jiroveci pneumonia and the introduction of effective combination anti-retroviral therapy (including highly active antiretroviral therapy [HAART]) have contributed to the reduced incidence of P. jiroveci pneumonia. Despite the success of these clinical interventions, P. jiroveci pneumonia remains the most common opportunistic pneumonia and the most common life-threatening infectious complication in HIV-infected patients. Trimethoprim/sulfamethoxazole (cotrimoxazole) remains the first-line agent for effective therapy and chemoprophylaxis, and corticosteroids represent an important adjunctive agent in the treatment of moderate-to-severe P. jiroveci pneumonia. However, problems of chemoprophylaxis and treatment failures, high rates of adverse drug reactions and drug intolerance to first-line antimicrobials, high rates of relapse or recurrence with second-line agents, and newer concerns about the development of P. jiroveci drug resistance represent formidable challenges to the management and treatment of AIDS-related P. jiroveci pneumonia. With the expanding global problem of HIV infection, the intolerance or unavailability of HAART to many individuals and limited access to healthcare for HIV-infected patients, P. jiroveci pneumonia will remain a major worldwide problem in the HIV-infected population. New drugs under development as anti-Pneumocystis agents such as echinocandins and pneumocandins, which inhibit beta-glucan synthesis, or sordarins, which inhibit fungal protein synthesis, show promise as effective agents. Continued basic research into the biology and genetics of P. jiroveci and host defense response to P. jiroveci will allow the development of newer antimicrobials and immunomodulatory therapeutic agents to more effectively treat life-threatening pneumonia caused by this organism.

Transgenic over-expression of MafK suppresses T cell proliferation and function in vivo

BACKGROUND

The small Maf proteins regulate gene transcription from Maf recognition elements (MARE). These proteins do not contain a canonical transactivation domain. Depending upon the ratio of small Maf proteins to their partner proteins, which either possess a transactivation domain or not, transcription can be switched on or off.

RESULTS

Transgenic mice were generated which over-express the small Maf family member MafK, specifically in the T cell lineage. It was our expectation that the high level of MafK would shift the balance to the formation of MafK homodimer and thereby repress MARE-dependent transcription. The transgenic mice had a shortened life span because of Pneumocystis carinii pneumonia and displayed a decrease in thymocytes and lower IL-2 and IL-4 mRNA expression levels. Analyses by electrophoretic gel mobility shift assay revealed that over-expressed MafK could interact with the proximal AP-1 sequence of IL-2 and the MARE in the IL-4 promoter region.

CONCLUSION

These results indicate that when over-expressed, MafK binds to a MARE-like sequence and represses MARE-dependent transcription. Consequently, T cell proliferation and cytokine secretion are affected. The MafK homodimer serves as an important molecular probe for evaluating the role played by cis-acting MAREs in the proliferation and function of T cells.

Modulation of allergic inflammation in mice deficient in TNF receptors

Tumor necrosis factor-alpha (TNF) is implicated as an important proinflammatory cytokine in asthma. We evaluated mice deficient in TNF receptor 1 (TNFR1) and TNFR2 [TNFR(-/-) mice] in a murine model of allergic inflammation and found that TNFR(-/-) mice had comparable or accentuated responses compared with wild-type [TNFR(+/+)] mice. The responses were consistent among multiple end points. Airway responsiveness after methacholine challenge and bronchoalveolar lavage (BAL) fluid leukocyte and eosinophil numbers in TNFR(-/-) mice were equivalent or greater than those observed in TNFR(+/+) mice. Likewise, serum and BAL fluid IgE; lung interleukin (IL)-2, IL-4, and IL-5 levels; and lung histological lesion scores were comparable or greater in TNFR(-/-) mice compared with those in TNFR(+/+) mice. TNFR(+/+) mice chronically treated with anti-murine TNF antibody had BAL fluid leukocyte numbers and lung lesion scores comparable to control antibody-treated mice. These results suggest that, by itself, TNF does not have a critical proinflammatory role in the development of allergic inflammation in this mouse model and that the production of other cytokines associated with allergic disease may compensate for the loss of TNF bioactivity in the TNFR(-/-) mouse.

Urokinase-type plasminogen activator in inflammatory cell recruitment and host defense against Pneumocystis carinii in mice

Effective host defense against Pneumocystis carinii depends upon the integrated actions of inflammatory cells and mediators in the lungs. Using immunocompetent and immunosuppressed mice, our laboratory has defined inflammatory changes in the lungs in response to P. carinii. However, the essential molecules and mechanisms required for cellular recruitment and for host defense against P. carinii are undefined. We hypothesized that urokinase-type plasminogen activator (uPA), a protease intimately involved in inflammatory cell migration and activation, is required for clearance of P. carinii. To test this hypothesis in vivo, we compared the intensity of P. carinii infection and inflammation in the lungs of mice lacking the uPA gene (uPA knockout mice) and in the lungs of wild-type mice. After intratracheal inoculation with P. carinii organisms, uPA knockout mice developed uniformly heavy P. carinii pneumonia while wild-type mice cleared the P. carinii inoculum. Bronchoalveolar lavage fluid from uPA knockout mice contained significantly smaller numbers of cells than did lavage fluid from wild-type mice. We conclude that deletion of the uPA gene prevents the clearance of P. carinii and reduces inflammatory cell recruitment. Therefore, uPA is an important participant in the network of inflammatory events required for the clearance of P. carinii, confirming an important role for this molecule in pulmonary host defense against opportunistic pathogens.

Susceptibility to Pneumocystis carinii in Mice Is Dependent on Simultaneous Deletion of IFN-γ and Type 1 and 2 TNF Receptor Genes

Pneumocystis carinii pneumonia is an important cause of morbidity and mortality in immunosuppressed patients, particularly HIV-infected individuals. An improved understanding of pulmonary host response, including the cytokines required for defense, could suggest novel immunotherapeutic approaches to this infection. The cytokines IFN-γ and TNF have contributory roles in host defense against P. carinii, but their combined and interactive importance is unclear. To test the roles of these cytokines in defense against P. carinii directly, organisms were inoculated intratracheally into wild-type mice and into three groups of gene-deleted mice: those lacking genes for IFN-γ (IFN-γ−/−), for TNF receptors 1 and 2 (TNFR−/−), and for both IFN-γ and TNFR (TNFR-IFN-γ−/−). Four weeks after P. carinii inoculation, lungs of the wild-type, IFN-γ−/−, and TNFR−/− mice demonstrated clearance of P. carinii and only mild inflammation. However, TNFR-IFN-γ−/− mice demonstrated severe P. carinii infection and lung inflammation. Our findings demonstrate conclusively that deletion of either IFN-γ or TNF activity alone does not block clearance of P. carinii. However, simultaneous deletion of IFN-γ and TNF receptor genes results in susceptibility to P. carinii. Rather than focusing exclusively on individual cytokines, our data suggest that immunotherapy targeted at maximizing both the IFN-γ and TNF responses to P. carinii may be required to augment host defense against this important opportunistic pathogen.

Activation and suppression of natural cellular immune functions by Pneumocystis carinii

The regulatory role of soluble cytokines in innate cellular immune responses induced by Pneumocystis carinii was assessed in vitro in direct comparison to induction by Listeria monocytogenes. This report shows that P. carinii organisms, as well as L. monocytogenes, stimulated in whole spleen cell cultures of SCID mice the release of IFN-gamma, TNF-alpha/beta, IL-10, IL-12, and iNO. This response was independent of functional T cells. Both macrophages (M phi) and natural killer (NK) cells were necessary for either microorganism to induce release of these cytokines. Cocultures of purified M phi--including alveolar M phi--and purified NK cells indicated that no other cell population was necessarily involved. Microbial induction of NK cell-derived IFN-gamma has been reported to be mediated by the combined effects of TNF-alpha and IL-12 released by M phi upon adequate microbial stimulation. Interestingly, only L. monocytogenes, but not P. carinii organisms could directly induce detectable amounts of TNF-alpha/beta, IL-12, or iNO in purified M phi cultures. In dose-response experiments, release of IFN-gamma, TNF-alpha/beta, and iNO was reduced at high relative concentrations of either microorganism. This high-dose suppression was at least partially controlled by M phi-produced IL-10. Our data show that, P. carinii potently induces activating and inhibitory innate cellular immune response mechanisms and indicate that the initial step of macrophage-mediated NK cell activation might also involve other pathways than those described to date.

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

Severe combined immunodeficient (scid) mice lack functional CD4+ lymphocytes, and therefore develop life-threatening Pneumocystis carinii infection. However, when scid mice are immunologically reconstituted with spleen cells, including CD4+ cells, a protective inflammatory response is mounted against the organism. To determine whether these lymphocytes induce elevated cytokine mRNA levels in response to P. carinii infection, steady-state levels of cytokine mRNAs were measured in the lungs of both reconstituted and unaltered scid mice. Despite significant numbers of organisms and the presence of functional alveolar macrophages in the lungs of 8- and 10-wk-old scid mice, there was neither evidence of pulmonary inflammation, nor increased proinflammatory cytokine expression. However, when 8-wk-old scid mice were immunologically reconstituted, signs of intense, focal pulmonary inflammation were observed, and levels of interleukin (IL)-1alpha, IL-1beta, IL-3, IL-6, interferon-gamma (IFN-gamma), tumor necrosis factor (TNF)-alpha, and TNF-beta mRNAs were all significantly elevated. Cytokine expression was increased at day 10 post-reconstitution (PR), maximal at day 12 PR, and returned to baseline by day 22 PR. In situ hybridization demonstrated that at day 12 PR, increased IL-1beta and TNF-alpha expression was localized to sites of intense inflammation and focal P. carinii colonization. Many of the cells expressing high levels of IL-1beta and TNF-alpha in these regions were in direct contact with organisms, or contained degraded organisms within their cytoplasm. Thus, even though functional macrophages are present in scid mice, CD4+ T cells are required for proinflammatory cytokine expression, which is associated with the generation of a protective inflammatory response at sites of P. carinii infection.

Role of gamma interferon in the host immune and inflammatory responses to Pneumocystis carinii infection

The role of gamma interferon (IFN-gamma) in host defense to Pneumocystis carinii was investigated by use of three different murine models of infection. C57BL/6 scid/scid (severe combined immunodeficient [SCID]) mice were given intratracheal inoculations of P. carinii and reconstituted with splenocytes from either mice with disrupted IFN-gamma genes (IFN-gamma-/- mice) or homozygous wild-type (IFN-gamma+/+) mice. Unreconstituted SCID mice had log10 7.08 +/- 0.13 P. carinii nuclei in their lungs at day 22 postinfection, whereas SCID mice reconstituted with splenocytes from either wild-type or IFN-gamma-/- mice had cleared the infection. However, there was a prolonged and exacerbated inflammatory response in the lungs of SCID mice reconstituted with IFN-gamma-/- splenocytes which was characterized by interstitial pneumonia, eosinophilia, and multinucleated giant cell formation. Similar results were found in C.B17 SCID mice reconstituted with CD4+ cells from P. carinii-immunized donors treated with neutralizing anti-IFN-gamma monoclonal antibody (MAb). These mice resolved their P. carinii infections; however, they also exhibited exacerbated lung pathology compared with mice treated with a control MAb. Finally, IFN-gamma-/- mice challenged intratracheally with P. carinii resolved their infection within 56 days as did IFN-gamma+/- mice. Furthermore, depletion of T cells in vivo with a MAb resulted in IFN-gamma-/- mice becoming susceptible to P. carinii infection. Together, these data indicate that IFN-gamma is not required for resolution of P. carinii infection; however, in the absence of IFN-gamma, there is a prolonged and exacerbated P. carinii-driven interstitial pneumonia characterized by eosinophilia and formation of multinucleated giant cells.

Development of an in vitro macrophage system to assess Penicillium marneffei growth and susceptibility to nitric oxide

We investigated the effect of nitric oxide (NO) and reactive nitrogen intermediates on the in vitro growth of Penicillium marneffei both in a cell-free system and in a novel macrophage culture system. In the cell-free system, NO that was chemically generated from NaNO2 in acid media (pH 4 and 5) markedly inhibited the growth of P. marneffei. On the contrary, inhibition of growth did not occur in neutral medium (pH 7.4) in which NO was not produced. P. marneffei conidia were phagocytized by nonstimulated murine J774 macrophages after 2 h of incubation. During the following 24 h, P. marneffei grew as yeast-like cells replicating by fission in the J774 macrophages. The intracellular growth of P. marneffei damaged nonstimulated J774 macrophages, as confirmed by electron microscopy. When J774 cells were stimulated by gamma interferon and lipopolysaccharide, which led to enhanced production of reactive nitrogen intermediates, the percentage of yeast-like cells was significantly reduced and P. marneffei conidia were damaged in the J774 macrophages. The inhibition of NO synthesis by N-monomethyl-L-arginine restored the intracellular growth of P. marneffei. The inverse correlation between intramacrophage growth and the amount of nitrite detected in culture supernatants supports the hypothesis that the L-arginine-dependent NO pathway plays an important role in the murine macrophage immune response against P. marneffei.

Role of CD8+ lymphocytes in host defense against Pneumocystis carinii in mice

An improved understanding of host defense against Pneumocystis carinii could provide novel therapeutic modalities directed against this opportunistic pathogen. Immunodeficient mouse models confirm the role of CD4+ lymphocytes in defense against P. carinii, but the role of CD8+ lymphocytes is controversial. BALB/c mice specifically depleted of CD4+ lymphocytes are susceptible to P. carinii, recruiting large numbers of CD8+ lymphocytes to their lungs during infection. Because of this recruitment, we hypothesized that CD8+ lymphocytes could participate in host defense against P. carinii. BALB/c mice were depleted of CD4+ lymphocytes, CD8+ lymphocytes, or both CD4+ and CD8+ lymphocytes. All mice were then inoculated intratracheally with P. carinii. Mice depleted of CD4+ lymphocytes became moderately infected with P. carinii. Mice depleted of CD8+ lymphocytes cleared the inoculum, indicating that CD8+ lymphocytes are unnecessary for defense when CD4+ lymphocytes are available. However, mice depleted of both CD4+ and CD8+ lymphocytes became significantly more intensely infected than mice depleted of CD4+ lymphocytes alone. Therefore, CD8+ lymphocytes participate in defense against P. carinii in vivo during depletion of CD4+ lymphocytes. To determine the mechanisms of this protection, CD8+ lymphocytes were purified from the lungs of CD4-depleted mice during infection. Lung CD8+ lymphocytes proliferated in response to P. carinii antigen and elaborated interferon-gamma in vitro. Thus CD8+ lymphocytes provide defense against P. carinii in vivo, and the elaboration of interferon-gamma likely represents one important mechanism of defense. During states of CD4+ lymphocyte depletion, the modulation of CD8+ lymphocyte function may provide alternative approaches to the host defense against opportunistic pathogens.