Acute eosinophilic pneumonia as a complication of influenza A (H1N1) pulmonary infection

Acute eosinophilic pneumonia (AEP) is a rare disease characterized by its acute onset and a clinical presentation simulating a bacterial pneumonia. Although it can be idiopathic, it has been described related to drugs, toxic agents and infections, mostly parasitic. We describe the case of influenza A (H1N1) severe pneumonia complicated by an acute eosinophilic pneumonia. Patient presented with respiratory failure and diffuse ground-glass opacities at chest-computed tomography. Clinical suspicion for this complication and bronchoalveolar lavage with cellular count analysis is crucial.

Acute and Chronic Airway Disease After Human Respiratory Syncytial Virus Infection in Cotton Rats (Sigmodon hispidus)

Infection with respiratory syncytial virus (RSV) generally presents as a mild, upper airway disease in human patients but may cause severe lower airway disease in the very young and very old. Progress toward understanding the mechanisms of RSV pathogenesis has been hampered by a lack of relevant rodent models. Mice, the species most commonly used in RSV research, are resistant to upper respiratory infection and do not recapitulate the pattern of virus spread in the human host. To address the need for better rodent models of RSV infection, we have characterized the acute and chronic pathology of RSV infection of a relatively permissive host, cotton rats (Sigmodon hispidus). We demonstrate that virus delivered to the upper airway results in widespread RSV replication in the ciliated respiratory epithelial cells of the nasal cavity and, to a lesser extent, of the lung. Although acute inflammation is relatively mild and rapidly eliminated after viral clearance, chronic, eosinophilic lung pathology persists. These data support the use of cotton rats as a robust rodent model of human RSV disease, including the association between RSV pneumonia and subsequent development of allergic asthma.

CD8 T cells inhibit respiratory syncytial virus (RSV) vaccine-enhanced disease

Vaccination of children with a formalin-inactivated (FI) respiratory syncytial virus (RSV) vaccine led to exacerbated disease including pulmonary eosinophilia following a natural RSV infection. Immunization of BALB/c mice with FI-RSV or a recombinant vaccinia virus (vv) expressing the RSV attachment (G) protein (vvG) results in a pulmonary Th2 response and eosinophilia after RSV challenge that closely mimics the RSV vaccine-enhanced disease observed in humans. The underlying causes of RSV vaccine-enhanced disease remain poorly understood. We demonstrate here that RSV M2-specific CD8 T cells reduce the Th2-mediated pathology induced by vvG-immunization and RSV challenge in an IFN-gamma-independent manner. We also demonstrate that FI-RSV immunization does not induce a measurable RSV-specific CD8 T cell response and that priming FI-RSV-immunized mice for a potent memory RSV-specific CD8 T cell response abrogates pulmonary eosinophilia after subsequent RSV challenge. Our results suggest that the failure of the FI-RSV vaccine to induce a CD8 T cell response may have contributed to the development of pulmonary eosinophilia and augmented disease that occurred in vaccinated individuals.

C5 modulates airway hyperreactivity and pulmonary eosinophilia during enhanced respiratory syncytial virus disease by decreasing C3a receptor expression

Enhanced respiratory syncytial virus disease, a serious pulmonary disorder that affected recipients of an inactivated vaccine against respiratory syncytial virus in the 1960s, has delayed the development of vaccines against the virus. The enhanced disease was characterized by immune complex-mediated airway hyperreactivity and a severe pneumonia associated with pulmonary eosinophilia. In this paper, we show that complement factors contribute to enhanced-disease phenotypes. Mice with a targeted disruption of complement component C5 affected by the enhanced disease displayed enhanced airway reactivity, lung eosinophilia, and mucus production compared to wild-type mice and C5-deficient mice reconstituted with C5. C3aR expression in bronchial epithelial and smooth muscle cells in the lungs of C5-deficient mice was enhanced compared to that in wild-type and reconstituted rodents. Treatment of C5-deficient mice with a C3aR antagonist significantly attenuated airway reactivity, eosinophilia, and mucus production. These results indicate that C5 plays a crucial role in modulating the enhanced-disease phenotype, by affecting expression of C3aR in the lungs. These findings reveal a novel autoregulatory mechanism for the complement cascade that affects the innate and adaptive immune responses.

Influenza A virus infection inhibits the efficient recruitment of Th2 cells into the airways and the development of airway eosinophilia

Most infections with respiratory viruses induce Th1 responses characterized by the generation of Th1 and CD8(+) T cells secreting IFN-gamma, which in turn have been shown to inhibit the development of Th2 cells. Therefore, it could be expected that respiratory viral infections mediate protection against asthma. However, the opposite seems to be true, because viral infections are often associated with the exacerbation of asthma. For this reason, we investigated what effect an influenza A (flu) virus infection has on the development of asthma. We found that flu infection 1, 3, 6, or 9 wk before allergen airway challenge resulted in a strong suppression of allergen-induced airway eosinophilia. This effect was associated with strongly reduced numbers of Th2 cells in the airways and was not observed in IFN-gamma- or IL-12 p35-deficient mice. Mice infected with flu virus and immunized with OVA showed decreased IL-5 and increased IFN-gamma, eotaxin/CC chemokine ligand (CCL)11, RANTES/CCL5, and monocyte chemoattractant protein-1/CCL2 levels in the bronchoalveolar lavage fluid, and increased airway hyperreactivity compared with OVA-immunized mice. These results suggest that the flu virus infection reduced airway eosinophilia by inducing Th1 responses, which lead to the inefficient recruitment of Th2 cells into the airways. However, OVA-specific IgE and IgG1 serum levels, blood eosinophilia, and goblet cell metaplasia in the lung were not reduced by the flu infection. Flu virus infection also directly induced AHR and goblet cell metaplasia. Taken together, our results show that flu virus infections can induce, exacerbate, and suppress features of asthmatic disease in mice.

IL-13 is sufficient for respiratory syncytial virus G glycoprotein-induced eosinophilia after respiratory syncytial virus challenge

Although well studied in settings of helminth infection and allergen sensitization, the combined contributions of IL-4 and IL-13 and their signaling pathways in models of viral pathogenesis have not been reported. Using a murine model of respiratory syncytial virus (RSV) infection, we evaluated the contribution of IL-13, alone and in conjunction with IL-4, during immunization with recombinant vaccinia virus expressing RSV G glycoprotein (vvGs) or with formalin-inactivated RSV (FI-RSV). We showed that both IL-4 and IL-13 activity must be inhibited to modulate G-specific responses resulting in severe RSV-induced disease. Inhibition of IL-4 or IL-13 activity alone had minimal impact on disease in vvGs-immunized mice. However, treatment of IL-4-deficient mice with IL-13Ra during vvGs immunization reduced IL-5, IL-13, and eotaxin production and pulmonary eosinophilia after RSV challenge. In contrast, FI-RSV-induced immune responses were diminished when either IL-4 or IL-13 activity was blocked. After RSV challenge, these type 2 T cell responses were also diminished in vvGs-primed IL-4Ralpha-deficient mice. Our data suggest that secreted vvGs uses mechanisms requiring signaling through the IL-4Ralpha-chain by either IL-4 or IL-13 for induction of eosinophilia and is the first description of the relative contributions of IL-4, IL-13, and their receptors in viral pathogenesis.

New IL-17 family members promote Th1 or Th2 responses in the lung: in vivo function of the novel cytokine IL-25

We have biologically characterized two new members of the IL-17 cytokine family: IL-17F and IL-25. In contrast to conventional in vitro screening approaches, we have characterized the activity of these new molecules by direct in vivo analysis and have compared their function to that of other IL-17 family members. Intranasal administration of adenovirus expressing IL-17, IL-17C, or IL-17F resulted in bronchoalveolar lavage neutrophilia and inflammatory gene expression in the lung. In contrast, intranasal administration of IL-25-expressing adenovirus or IL-25 protein resulted in the production of IL-4, IL-5, IL-13, and eotaxin mRNA in the lung and marked eosinophilia in the bronchoalveolar lavage and lung tissue. Mice given intranasal IL-25 also developed epithelial cell hyperplasia, increased mucus secretion, and airway hyperreactivity. IL-25 gene expression was detected following Aspergillus and Nippostrongylus infection in the lung and gut, respectively. IL-25-induced eosinophilia required IL-5 and IL-13, but not IL-4 or T cells. Following IL-25 administration, the IL-5(+) staining cells were CD45R/B220(+), Thy-1(+/-), but were NK1.1-, Ly-6G(GR-1)-, CD4-, CD3-, and c-kit-negative. gamma-common knockout mice did not develop eosinophilia in response to IL-25, nor were IL-5(+) cells detected. These findings suggest the existence of a previously unrecognized cell population that may initiate Th2-like responses by responding to IL-25 in vivo. Further, these data demonstrate the heterogeneity of function within the IL-17 cytokine family and suggest that IL-25 may be an important mediator of allergic disease via production of IL-4, IL-5, IL-13, and eotaxin.

Eosinophils, eosinophil ribonucleases, and their role in host defense against respiratory virus pathogens

Eosinophils remain among the most enigmatic of cells, as our appreciation of their detrimental activities--e.g., asthma and allergic disease--far outweighs our understanding of their beneficial effects. Among the major secretory effector proteins of eosinophils are the ribonucleases eosinophil-derived neurotoxin (EDN) and eosinophil cationic protein (ECP) in primates and their orthologs, the eosinophil-associated ribonucleases (EARs) in rodents. The rapid diversification observed among these ribonucleases suggested that the ultimate target(s) might be similarly efficient at generating sequence diversity while maintaining an unalterable susceptibility to ribonucleolytic cleavage. This has prompted us to consider a role for these proteins and by extension, for eosinophils, in host defense against single-stranded RNA virus pathogens. We detail our studies of the antiviral activity of eosinophils and eosinophil ribonucleases against respiratory syncytial virus (RSV) in vitro and the related, natural rodent pathogen, pneumonia virus of mice (PVM), in vivo, and consider the possibility that antiviral host defense and the dysregulated responses leading to asthma represent opposing sides of an eosinophil-mediated double-edged sword.

CpG containing oligodeoxynucleotides are potent adjuvants for parenteral vaccination with the fusion (F) protein of respiratory syncytial virus (RSV)

The feasibility of using oligodeoxynucleotides (ODN) containing unmethylated CpG motifs as parenteral adjuvants for subunit vaccines against RSV was tested in BALB/c mice. Compared with immunization with natural F protein adsorbed to aluminum hydroxide (F/AlOH) adjuvant alone, coadministration of F/AlOH with CpG ODN resulted in statistically significant increases in serum neutralization titers, an enhanced generation of splenic antigen-dependent killer cell precursors, and accelerated clearance of infectious virus from lungs 4 days after challenge. The statistically significant increases in serum IFNgamma and anti-F protein IgG2a titers, and significantly diminished pulmonary IL-5 and eosinophilia after challenge indicated that CpG ODN enhanced the ability of F/AlOH to elicit type 1 immune responses. F protein-specific serum IgE titers were also reduced. Further analysis of pulmonary inflammatory cells demonstrated an expansion of CD8(+) T cells, relative to the CD4(+) T cell compartment. The potency of CpG ODN was not adversely affected in gene knockout mice devoid of the p35 chain of the IL-12 heterodimer. Taken together, the results suggest a novel formulation for naïve recipients of F protein-based subunit vaccines that does not result in a type 2 phenotype.

IL-12-activated NK cells reduce lung eosinophilia to the attachment protein of respiratory syncytial virus but do not enhance the severity of illness in CD8 T cell-immunodeficient conditions

Bronchiolitis caused by respiratory syncytial virus (RSV) infection is a major cause of hospitalization in children under 1 year of age. RSV causes common colds in older children and adults, but can cause serious disease in immunodeficient patients and the elderly. Development of effective vaccines and treatments for RSV infection is therefore a priority. Because bronchiolitis and vaccine-augmented disease are thought to be caused by exuberant T cell activation, attention has focused on the use of immunomodulators that affect T cell responses. In mice, IL-12 treatment down-regulates type 2 cytokine responses to the attachment protein G of RSV, reducing lung eosinophilia but further enhancing illness. We now show that CD8(+) T cells are responsible for enhanced weight loss, whereas IL-12-activated NK cells express high levels of IFN-gamma and inhibit lung eosinophilia without causing illness. Moreover, unlike immunocompetent mice, virus is detected in the mediastinal lymph nodes after elimination of both CD8(+) T cells and NK cells. These studies show that innate immune responses to viral infections direct the pattern of subsequent specific immunity and are critical to the development of nonpathogenic antiviral effects. We speculate that IL-12 treatment might be beneficial and safe in T cell-deficient patients with RSV pneumonitis.

DNA encoding the attachment (G) or fusion (F) protein of respiratory syncytial virus induces protection in the absence of pulmonary inflammation

Significant protection against respiratory syncytial virus (RSV) infection was induced in mice vaccinated intramuscularly (i.m.) with DNA encoding the F or G protein of RSV. The amounts of IgG1 of IgG2a antibodies in mice immunized with DNA-G alone were similar. However, the antibody response in mice co-immunized with DNA-G and DNA encoding IL-4 (DNA-IL-4) was strongly biased towards IgG1. In contrast, the antibody response in mice co-immunized with DNA-G and DNA-IL-2, -IL-12 or-IFN-gamma was biased towards IgG2a. Mice vaccinated with DNA-F either alone or in combination with DNA encoding cytokines developed a predominant RSV-specific IgG2a response, which was most pronounced in mice co-immunized with DNA-F and DNA-IL-12 or -IFN-gamma. Vaccinated mice developed only a slightly enhanced pulmonary inflammatory response following RSV challenge. More significantly, and in contrast to mice scarified with recombinant vaccinia virus expressing the G protein, mice vaccinated i.m. with DNA-G did not develop pulmonary eosinophilia, even when the immune response was biased towards a Th2 response by co-administration of DNA-IL-4.

Type 4 phosphodiesterase inhibitors attenuate respiratory syncytial virus-induced airway hyper-responsiveness and lung eosinophilia

Viral respiratory infections are considered one of the triggers of exacerbations of asthma. In a model of virus-induced airway hyper-responsiveness (AHR), mice infected with human respiratory syncytial virus (RSV) were shown to develop AHR accompanied by lung eosinophilia. Inhibitors of cyclic nucleotide phosphodiesterase (PDE) have been shown to affect airway responsiveness and pulmonary allergic inflammation. In this study, we assessed the effects of type 4 PDE (PDE4) inhibitors on AHR following RSV infection and compared them with a PDE3 inhibitor. In mice infected by intranasal inoculation of RSV, treatment with the PDE4 inhibitor rolipram or Ro-20-1724 reduced both AHR and the eosinophil infiltration of the airways. In contrast, the PDE3 inhibitor, milrinone, did not influence airway responsiveness or eosinophilic inflammation. These results demonstrate that PDE4 inhibitors can modulate RSV-induced AHR and lung eosinophilia and indicate that they have a potential role in treating exacerbations of asthma triggered by viral infection.

Atypical pulmonary eosinophilia is mediated by a specific amino acid sequence of the attachment (G) protein of respiratory syncytial virus

We analyzed the immune responses evoked by a series of overlapping peptides to better understand the molecular basis for respiratory syncytial virus (RSV) G protein-induced eosinophilia in BALB/c mice. In vitro stimulation of spleen cells from natural G protein-primed mice showed dominant proliferative and cytokine (interferon [IFN]-gamma and interleukin [IL]-5) responses to a peptide encompassing amino acids 184-198. Mice vaccinated with peptide 184- 198 conjugated to keyhole limpet hemocyanin showed significant pulmonary eosinophilia (39.5%) after challenge with live RSV. In contrast, mice immunized with a peptide (208-222) conjugate associated with induction of IFN-gamma secreting spleen cells did not exhibit pulmonary eosinophilia after challenge. The in vivo depletion of CD4(+) cells abrogated pulmonary eosinophilia in mice vaccinated with the peptide 184-198 conjugate, whereas the depletion of CD8(+) cells had a negligible effect. Therefore, we have identified an association between peptide 184- 198 of natural G protein and the CD4(+) T cell-mediated induction of pulmonary eosinophilia after live RSV challenge. Out of 43 human donors, 6 provided peripheral blood mononuclear cells that showed reactivity to G protein from RSV A2, 3 of which responded to peptide 184- 198. The results have important implications for the development of a vaccine against RSV.

Abundant IFN-gamma production by local T cells in respiratory syncytial virus-induced eosinophilic lung disease

Respiratory syncytial virus (RSV) is a frequent cause of severe lung disease in young children. Primed T cells are required for virus clearance, but are causally implicated in the enhanced pathology seen following RSV infection of some infants and experimental animals vaccinated against the virus. In BALB/c mice, vaccination with recombinant vaccinia virus expressing the viral attachment protein (G) leads to pulmonary eosinophilia during subsequent infection, which indirect evidence suggests may be due to CD4+ Th2 cells. The production of IFN-gamma, IL-2, -4, -5 and -10 cytokine mRNA by RT-PCR and intracellular cytokines by flow cytometry following RSV challenge of vaccinated mice were therefore compared. Lung eosinophilia was associated with enhanced local recruitment of CD4+ cells in G sensitized mice, while CD8+ cells dominated in mice vaccinated with the viral fusion protein (F) or second matrix protein (M2). Lung eosinophilia was also associated with a localized reduction in IFN-gamma and increased IL-4 and IL-5 mRNA transcription as well as elevated RSV specific IgG1 antibody production. Th2 cytokine protein production by T cells showed no apparent change. Although IFN-gamma production diminished in eosinophilic mice, it remained the major cytokine found in lung T cells. It was concluded that lung eosinophilia can develop despite abundant IFN-gamma production by local T cells, but is associated with a shift in the balance between Th2 and Th1 cytokine production.

Virus-specific CD8+ T lymphocytes downregulate T helper cell type 2 cytokine secretion and pulmonary eosinophilia during experimental murine respiratory syncytial virus infection

T lymphocytes play a pivotal role in the immune response during viral infections. In a murine model of experimental respiratory syncytial virus (RSV) infection, mice sensitized to either of the two major glycoproteins of RSV develop distinct patterns of cytokine secretion and lung inflammation upon subsequent RSV infection. Mice sensitized to RSV-G (attachment) glycoprotein exhibit a strong interleukin (IL)-4 and IL-5 response and develop pulmonary eosinophilia, whereas mice sensitized to RSV-F (fusion) glycoprotein develop a predominantly T helper cell (Th)1 response and pulmonary inflammation characterized by mononuclear cell infiltration. In this study, we examined the potential role of virus-specific CD8+ T cytolytic T cells on the differentiation and activation of functionally distinct CD4+ T cells specific to these viral glycoproteins. Mice primed with recombinant vaccinia virus expressing RSV-F glycoprotein mounted a strong RSV-specific, MHC class I-restricted cytolytic response, whereas priming with recombinant vaccinia virus expressing RSV-G glycoprotein failed to elicit any detectable cytolytic response. Priming for a RSV-specific CD8+ T cell response, either with a recombinant vaccinia virus expressing RSV-G glycoprotein in which a strong CD8+ T cell epitope from RSV-M2 (matrix) protein has been inserted or with a combination of vaccinia virus expressing the matrix protein and the RSV-G glycoprotein, suppressed the eosinophil recruitment into the lungs of these mice upon subsequent challenge with RSV. This reduction in pulmonary eosinophilia correlated with the suppression of Th2 type cytokine production. The importance of CD8+ T cells in this process was further supported by the results in CD8+ T cell deficient, beta 2 microglobulin KO mice. In these mice, priming to RSV-F glycoprotein (which in normal mice primed for a strong cytolytic response and a pulmonary infiltrate consisting primarily of mononuclear cells on RSV challenge) resulted in the development of marked pulmonary eosinophilia that was not seen in mice with an intact CD8+ T cell compartment. These results indicate that CD8+ T cells may play an important role in the regulation of the differentiation and activation of Th2 CD4+ T cells as well as the recruitment of eosinophils into the lungs during RSV infection.