Dual Proinflammatory and Antiviral Properties of Pulmonary Eosinophils in Respiratory Syncytial Virus Vaccine-Enhanced Disease

Abstract

Human respiratory syncytial virus (RSV) is a major cause of morbidity and severe lower respiratory tract disease in the elderly and very young, with some infants developing bronchiolitis, recurrent wheezing, and asthma following infection. Previous studies in humans and animal models have shown that vaccination with formalin-inactivated RSV (FI-RSV) leads to prominent airway eosinophilic inflammation following RSV challenge; however, the roles of pulmonary eosinophilia in the antiviral response and in disease pathogenesis are inadequately understood. In vivo studies in mice with eotaxin and/or interleukin 5 (IL-5) deficiency showed that FI-RSV vaccination did not lead to enhanced pulmonary disease, where following challenge there were reduced pulmonary eosinophilia, inflammation, Th2-type cytokine responses, and altered chemokine (TARC and CCL17) responses. In contrast to wild-type mice, RSV was recovered at high titers from the lungs of eotaxin-and/or IL-5-deficient mice. Adoptive transfer of eosinophils to FI-RSV-immunized eotaxin-and IL-5-deficient (double-deficient) mice challenged with RSV was associated with potent viral clearance that was mediated at least partly through nitric oxide. These studies show that pulmonary eosinophilia has dual outcomes: one linked to RSV-induced airway inflammation and pulmonary pathology and one with innate features that contribute to a reduction in the viral load. IMPORTANCEThis study is critical to understanding the mechanisms attributable to RSV vaccine-enhanced disease. This study addresses the hypothesis that IL-5 and eotaxin are critical in pulmonary eosinophil response related to FI-RSV vaccine-enhanced disease. The findings suggest that in addition to mediating tissue pathology, eosinophils within a Th2 environment also have antiviral activity. R espiratory syncytial virus (RSV) is a serious lower respiratory tract infection in infants, the elderly, and the immunocompromised (1-4), resulting in Ͼ130,000 hospitalizations in the United States each year (5, 6). Children who experience acute RSV infection of the lower respiratory tract have an increased likelihood of developing childhood asthma (7). To date, there is no safe and effective RSV vaccine available. This is in part linked to the negative outcome of a 1960s clinical trial using a formalin-inactivated alum-precipitated RSV (FI-RSV) vaccine (8). Children immunized with the FI-RSV vaccine experienced more severe disease following subsequent natural exposure to RSV, with one study showing 69% of immunized children developing pneumonia compared to only 9% of children in the unimmunized control group (9). In a second study, 80% of FI-RSV-immunized infants were hospitalized and two died, compared with only 5% hospitalization and no death in the control group (10). FI-RSV vaccineenhanced illness was clinically characterized as severe primary RSV infection, with bronchiolitis, hypoxemia, and pneumonia. However, in contrast to the neutrophilic inflammation observed during primary RSV infection, the more severe a...

Role of nitric oxide in immune responses against viruses: beyond microbicidal activity

“…Mice deficient in these two mediators not only have lower eosinophilic inflammatory infiltrate in RSV infection, but they also have more difficulty in eliminating the virus. The transfer of eosinophils to these animals participated in more rapid viral clearance, while treatment with L-NMA reversed this transfer, reaffirming the importance of NO produced by eosinophils in the resolution of this infection [20]. Because RSV infection is more frequent and more severe early in life, efforts have been undertaken to develop a vaccine able to generate protective antibody titers in children.…”

“…In the immune system, the reaction of NO with cysteine and thiol residues could modify the pattern of immune [20] Coxsackievirus NO nitrosylates coxsackievirus protease, decreasing its enzymatic activity and interrupting the viral cycle [52] HIV-1 NO donors can nitrosylate the reverse transcriptase from HIV-1 in a dose-dependent manner in vitro, decreasing HIV replication [53] Impairment Influenza Treatment of infected mice with L-NMMA increased survival and delayed the development of pneumonia, although it did not decrease viral replication [29] DENV-3 NO collaborates in neurological impairment caused by DENV. iNOS-deficient mice survive longer and has no brain damage [35] HIV-1 NO in the central nervous system can react with superoxide anion (O 2 -) and form peroxynitrite, an extremely toxic radical to neurons [41]…”

A critical role of Gas6/Axl signal in allergic airway responses during RSV vaccine‐enhanced disease

“…A mouse FI‐RSV VED model has been established and widely used to clarify the mechanism underlying the pathogenesis of RSV‐associated allergy 40 , 41 , 42 . The structural changes in RSV‐F protein that result from formalin fixation have been considered one of the causes of FI‐RSV VED.…”

Immunogenicity of an adeno-vector vaccine expressing the F protein of a respiratory syncytial virus manufactured from serum-free suspension culture

“…The severity of inflammation in the H/E-stained sections was scored by following the reported criteria; grade 1: mixed mononuclear cell infiltrate next to bronchus; grade 2: diffuse monocyte Infiltration in alveolar spaces; grade 3: mixed diffuse infiltrate and small focus of BALT; grade 4: extensive dense collection of mixed mononuclear cells (BALT) as well as diffuse infiltrate (Brincks et al, 2013). The degree of airway mucus occlusion were scored by following the reported criteria; 0: signified no occlusion; 1: small areas of luminal accumulation of mucus; 2: partial occlusion of at least one small airway; and 3: complete occlusion of at least one small airway (Su et al, 2015).…”

“…The sections were stained with 1% H/E, or monoclonal rat IgG anti-major basic protein (MBP; provided by Dr. James J. Lee, Mayo Clinic, AZ, USA) for eosinophil followed by the appropriate secondary antibodies, or periodic acid-Schiff (PAS) dye (Cat. 395B-1, SigmaeAldrich) which reacted with pulmonary mucin for airway mucus secretion (Su et al, 2015). Twenty bright-field pictures of each section were obtained at 100Â and 200Â magnification (Nikon DXM1200 CCD digital camera), and the number of eosinophils in the high-power field (HPF) was counted.…”