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* Interdisciplinary Graduate Program in Immunology,
Department of Pathology, and
Department of Microbiology, University of Iowa, Iowa City, IA 52242
| Abstract |
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, which is produced following STAT4 activation, contributes to clinical illness and increased Penh, but not weight loss. Our results have important implications for future RSV vaccine design, suggesting that enhancing a Th1 response may exacerbate disease. | Introduction |
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55% of the vaccines examined (3). Based on the previous experience with FI-RSV immunization in humans, the development of pulmonary eosinophilia has become the hallmark of RSV vaccine-enhanced disease. However, the extent to which eosinophils directly contribute to the pathogenesis of RSV vaccine-enhanced disease has not been firmly established.
We have previously demonstrated that the Th2 cell-associated cytokine IL-13 is necessary for the development of pulmonary eosinophilia upon RSV challenge of mice previously immunized with a recombinant vaccinia virus (vacv) expressing the attachment (G) protein of RSV (vacvG) (4). In this report, we examined STAT6-deficient mice to determine if either IL-4 or IL-13 contributed to the development of increased weight loss, clinical illness, and enhanced pause (Penh) after RSV challenge of mice previously immunized with vacvG. We show that STAT6 is necessary for the development of pulmonary eosinophilia, but that it is not required for increased weight loss, clinical illness, and Penh after RSV challenge of mice previously immunized with vacvG. Because eosinophilia is considered the hallmark of RSV vaccine-enhanced disease, we verified our results using
dblGATA mice, which are deficient in the generation of eosinophils (5). At the same time, we examined STAT4-deficient mice to determine the contribution of Th1 cell-associated signaling to the development of RSV vaccine-enhanced weight loss, clinical illness, and Penh. Our results demonstrate that the transcription factor STAT4 is required for the development of weight loss, clinical illness, and increased Penh. Assessing the role of IFN-
, a cytokine produced in response to STAT4 activation, our data indicates that the production of IFN-
contributes to clinical illness and increased Penh, but not weight loss. Our results demonstrate that eosinophils are not required for the development of increased weight loss, clinical illness, or Penh after RSV challenge of mice previously immunized with vacvG.
| Materials and Methods |
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BALB/cAnNCr mice were purchased from the National Cancer Institute (Bethesda, MD). STAT4-deficient mice (C.129S2-Stat4tm1Gru/J), STAT6-deficient mice (C.129S2-Stat6tm1Gru/J), IL-12p40-deficient mice (C.129S1-Il12btm1Jm/J), IFN-
-deficient mice (C.129S7(B6)-Ifngtm1Ts/J), and
dblGATA mice (C.Cg-Gata1tm6Sho/J), all on a BALB/c background, were purchased from The Jackson Laboratory. All experimental procedures were approved by the University of Iowa Animal Care and Use Committee (Iowa City, IA).
Viruses
Recombinant vacv and the A2 strain of RSV were propagated as previously described (4). Virus titers were determined by plaque assay as previously described (6).
Infection of mice and measurement of systemic disease
Mice were immunized with 3 x 106 PFU of a recombinant vacv expressing β-galactosidase (vacvβ-gal) or vacvG and challenged with 2–3 x 106 PFU of RSV as previously described (4). Weight loss and clinical illness scores were determined on a daily basis following RSV challenge as previously described (4).
Detection of eosinophils
Cells in the bronchioalveolar lavage (BAL) and lung were harvested as previously described (6). BAL and lung cells were counted and stained as previously described (6) with anti-Siglec-F PE, anti-CD11c allophycocyanin, and anti-CD45 PE-Cy7. Cells staining positive for CD45 were gated and examined for Siglec-F and CD11c expression. A distinct population of cells staining Siglec-F+ and CD11clow were identified in vacvG- but not vacvβ-gal-immunized wild-type (WT) mice. These cells have previously been identified as eosinophils (7). The total number of eosinophils in the BAL and lung was calculated based on cell counts and the percentages obtained from flow cytometry. Cells were collected on a FACSCanto (Becton Dickinson) and analyzed using Flow Jo software (Tree Star).
Measurement of airway resistance
Penh was measured using a whole body plethysmograph (Buxco Electronics). Baseline Penh values for each mouse were recorded before and on a daily basis following RSV infection.
Statistics
Statistical analyses were performed using GraphPad InStat software.
| Results and Discussion |
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To evaluate the contribution of Th2 cells to RSV vaccine-enhanced disease, we examined the necessity of STAT6, a transcription factor activated after IL-4 and/or IL-13 cytokine stimulation, that plays a critical role in Th2 cell differentiation (8). The number of eosinophils in the BAL and lung were determined 7 days after RSV challenge of mice previously immunized with either vacvG or vacvβ-gal as a control. As expected, vacvG-immunized WT mice undergoing a challenge RSV infection developed increased pulmonary eosinophilia in both the BAL and lung as compared with mice undergoing a primary RSV infection (vacvβ-gal-immunized). In contrast, vacvG-immunized STAT6-deficient mice had significantly decreased pulmonary eosinophilia in both the BAL (Fig. 1A) and lung (Fig. 1B) after RSV challenge as compared with WT mice. As an additional control, mice deficient in STAT4 were also examined and were found to have no significant alteration in the development of pulmonary eosinophilia as compared with WT mice. These data support our previous work (4) and suggest that IL-13 signaling through STAT6 is necessary for the development of pulmonary eosinophilia in vacvG-immunized mice undergoing a challenge RSV infection.
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To determine the contribution of Th2 cell-associated signaling through STAT6 to the development of RSV vaccine-enhanced systemic disease, weight loss and clinical illness scores were recorded on a daily basis after RSV challenge of STAT6-deficient mice previously immunized with vacvG. In addition, we examined vacvG-immunized STAT4-deficient mice to determine the relative contribution of Th1 cell-associated signaling to RSV vaccine-enhanced disease. Weight loss (Fig. 2A) and clinical illness scores (Fig. 2B) observed in STAT6-deficient mice were not significantly different from those in WT mice. However, as early as day 2 postinfection, STAT4-deficient mice exhibited significantly reduced weight loss and clinical illness as compared with WT mice. These data indicate that signaling through STAT4 is necessary for the development of RSV vaccine-enhanced systemic disease in vacvG-immunized mice undergoing a challenge RSV infection.
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Eosinophils are not necessary for increased weight loss, clinical illness, or Penh
To more directly test whether or not eosinophils were necessary for weight loss, clinical illness, or increased Penh, we examined
dblGATA mice that cannot generate eosinophils from their bone marrow precursors due to the deletion of a palindromic binding site in the proximal promoter of the GATA-1 gene (5). Fig. 3A shows that RSV-induced weight loss is comparable between both vacvG-immunized
dblGATA and WT mice. In addition,
dblGATA mice exhibit increased clinical illness (Fig. 3B) and Penh (Fig. 3C) similar to what is observed in WT mice. These data demonstrate that eosinophils are not required for increased weight loss, clinical illness, and Penh, the disease parameters most often associated with RSV vaccine-enhanced disease in this model.
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production contributes to clinical illness and increased Penh, but not weight loss
Activation of the transcription factor STAT4 augments IFN-
production by Th1 cells (9). To determine the impact of IFN-
production on RSV vaccine-enhanced disease, we examined weight loss, clinical illness, and Penh after RSV challenge of IFN-
-deficient mice previously immunized with vacvG. Consistent with previous data demonstrating a requirement for TNF-
in mediating weight loss in this model (10), Fig. 4A demonstrates that in the absence of IFN-
, weight loss is not significantly altered. However, both clinical illness (Fig. 4B) and Penh (Fig. 4C) were decreased in IFN-
-deficient mice as compared with WT mice. However, because this reduction was not complete, these data indicate that IFN-
contributes to, but is not the sole mediator of, clinical illness and increased Penh in vacvG-immunized mice undergoing RSV challenge. Thus, it is likely that additional cytokines such as TNF-
may also contribute to the development of clinical illness and increased Penh in this model. Taken together, these data suggest that the activation of STAT4 leads to the production of IFN-
and the subsequent development of clinical illness and increased Penh, as well as the production of TNF-
and the subsequent development of weight loss after RSV challenge of mice previously immunized with vacvG. Interestingly, depletion of IL-4 from FI-RSV-immunized mice has been shown to reduce weight loss upon RSV challenge (11). The cytokine requirements for the development of pulmonary eosinophilia have been found to differ between vacvG- and FI-RSV-immunized mice (4, 12). Thus, the cytokines responsible for inducing weight loss in each of these models may also differ.
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The development of pulmonary eosinophilia has often been used as a hallmark of RSV vaccine-enhanced disease. However, the direct contribution of eosinophils to the development of RSV vaccine-enhanced disease has not been previously examined. Our data demonstrate that eosinophils do not contribute to multiple disease parameters including increased weight loss, clinical illness, and Penh upon RSV challenge of mice previously immunized with vacvG. The presence of eosinophils in the RSV-infected lung appears to be primarily a consequence of the induction of a relatively low number of RSV-specific memory Th2 cells rather than a direct cause of significant pathology. Instead, our data suggest that signaling through STAT4 leads to increased weight loss, clinical illness, and Penh upon RSV challenge of mice previously immunized with vacvG.
The data presented here have important implications for future RSV vaccine design. Due to the previous notion that Th2 cells and eosinophils directly contributed to the development of RSV vaccine-enhanced disease, much effort in RSV vaccine design has gone into developing vaccination strategies to favor the induction of highly skewed RSV-specific Th1 responses. Our data demonstrate that eosinophils do not directly contribute to RSV vaccine-enhanced disease and indicate that RSV vaccine-enhanced disease is the result of an exuberant RSV-specific memory Th1 cell response. Importantly, it is not the magnitude of the overall inflammation but the character of the immune response that dictates immunopathology. Thus, either skewing the RSV-specific memory CD4 T cell response to predominately a Th1 response or blocking the Th2 memory response altogether would not prevent the development of RSV-induced disease but could, in fact, induce exacerbated disease. Our results suggest that future RSV immunization strategies should strive to achieve a balanced immune response.
| Acknowledgments |
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| Disclosures |
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| Footnotes |
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1 This work was supported by funding by American Heart Association Midwest Affiliate Predoctoral Fellowship 0815540G (to E.M.C.), Department of Pathology Start-Up Funds (to K.L.L.), and National Institutes of Health Grant AI 063520 (to S.M.V.). ![]()
2 Address correspondence and reprint requests to Dr. Steven M. Varga, Department of Microbiology, 51 Newton Road, University of Iowa, Iowa City, IA 52242. E-mail address: steven-varga{at}uiowa.edu ![]()
3 Abbreviations used in this paper: RSV, respiratory syncytial virus; BAL, bronchoalveolar lavage; FI, formalin inactivated; Penh, enhanced pause; vacv, vaccinia virus; vacvG, vacv expressing RSV attachment (G) protein; vacvβ-gal, vacv expressing β-galactosidase; WT, wild type; KO, knockout. ![]()
4 The online version of this article contains supplemental material. ![]()
Received for publication July 30, 2008. Accepted for publication September 17, 2008.
| References |
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response to viral infection. Science 297: 2063-2066. This article has been cited by other articles:
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C. M. Percopo, Z. Qiu, S. Phipps, P. S. Foster, J. B. Domachowske, and H. F. Rosenberg Pulmonary Eosinophils and Their Role in Immunopathologic Responses to Formalin-Inactivated Pneumonia Virus of Mice J. Immunol., July 1, 2009; 183(1): 604 - 612. [Abstract] [Full Text] [PDF] |
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M. R. Olson and S. M. Varga Fas Ligand Is Required for the Development of Respiratory Syncytial Virus Vaccine-Enhanced Disease J. Immunol., March 1, 2009; 182(5): 3024 - 3031. [Abstract] [Full Text] [PDF] |
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