Eosinophils contribute to innate antiviral immunity and promote clearance of respiratory syncytial virus.

TLDR: It is demonstrated that eosinophils can protect against RSV in vivo, as they promote virus clearance and may thus limit virus-induced lung dysfunction.

About: This article is published in Blood.The article was published on 2007-09-01 and is currently open access. It has received 249 citations till now. The article focuses on the topics: Virus & Interleukin 5.

Figures

Figure 1. Hypereosinophilic mice show accelerated viral clearance in the lung. (A) WT (E) and hypereosinophilic (IL-5 Tg; F) mice were inoculated with RSV at day 0 and viral clearance or (B) increases in numbers of mucus-secreting cells per 100 m of airway epithelial basement membrane monitored at the times indicated. (C) Eosinophils (5 106 cells) isolated from hypereosinophilic mice were adoptively transferred to WT mice 2 hours prior to inoculation with RSV. Viral titer was determined at 6 dpi. Bars represent the median value. (D) WT or dblGATA mice were inoculated with RSV and viral titer quantified at 5 dpi. Data represent the mean plus or minus SEM (n 3-6 mice per experimental group). Bars represent the median value. *P .05; **P 0.01; ***P .001.

Figure 4. Adoptive transfer of WT but not MyD88-deficient eosinophils significantly accelerates viral clearance and suppresses RSV-induced AHR.

Figure 5. RSV infection increases the expression of antiviral genes, and the inhibition of NOS-2 abrogates the protection conferred by eosinophils. (A) FACS-purified splenic eosinophils were isolated from naive hypereosinophilic mice (u) or hypereosinophilic (f) and hypereosinophilic MyD88-deficient (o) mice at 1 dpi, and expression of indicated genes were analyzed by quantitative RT-PCR. All quantitative assessments were normalized to HPRT, and fold induction was calculated relative to naive hypereosinophilic mice. *Comparison between naive and RSV inoculated hypereosinophilic mice. #Comparison between RSVinoculated hypereosinophilic and hypereosinophilic MyD88 / mice. (B) WT (E) and hypereosinophilic (F) mice were inoculated, lung samples were collected at the indicated times after infection, and expression of indicated genes were analyzed by quantitative RT-PCR. (C) WT and hypereosinophilic mice were pretreated with L-NMA (f) or D-NMA (u) prior to inoculation with RSV. Lung viral titer was measured at 3 dpi (n 3-6 mice). *P .05; #P .05; **P .01; ##P .01; ***P .001; ###P .001. Error bars are SEM.

Figure 3. ssRNA-induced activation of eosinophils. (A) Isolated splenocytes from hypereosinophilic mice were activated with ssRNA for 10 minutes, and peroxidase activity was measured to determine EPO release. (B) FACS-purified eosinophils were stimulated with medium (Bi-Bii) or ssRNA (1 g/ mL) (Biii, Biv) for 10 minutes, then changes in ultrastructural morphology were examined by electron microscopy. Arrows demarcate secondary granules, with irregular or faded electron-dense cores documenting degranulation in a representative micrograph. Scale bar equals 1 M (left panels) and 2 M (right panels) see “Materials and methods, Electron microscopy” for detailed image acquisition information. (C) Isolated mixed splenocytes from hypereosinophilic mice were treated with ssRNA for 10 minutes, then stained for CD11b expression. A representative histogram gated on eosinophils is presented in the left panel. The MFI of CD11b expression is shown in the right panel. These data were collected on a FACSort. (D) Eosinophils were isolated from hypereosinophilic MyD88-sufficient or -deficient mice and treated with ssRNA (1 g/mL) for 10 minutes, then stained for CD11b expression. These data were collected on a BD CANTO. Data represent the mean plus or minus SEM (n 3-8 mice per experimental group). **P .01; ***P .001; ###P .001.

Figure 2. Eosinophils express surface and intracellular toll-like receptors. (A) Eosinophils from the spleens of hypereosinophilic mice were identified by CCR3 expression and high side scatter and stained for TLR-3, TLR-4, and TLR-7. Dashed lines denote isotype control (and were similar to unstained cells); solid lines represent respective TLR antibody. To detect intracellular TLR expression, splenocytes were pretreated with saponin. (B) Summary of mean fluorescence intensity (MFI) of surface and intracellular TLR expression by splenic eosinophils. The mean of 3 independent experiments is shown. (C) Neutrophils (Neuts) and eosinophils (Eos) were identified in the lungs of hypereosinophilic mice by scatter properties (left panel) and Gr-1 expression (middle panel). Comparative MFI of TLR-7 expression on neutrophils (N) and eosinophils (E) is shown in the right panel. Data represent the mean plus or minus SEM (n 3-8 mice per experimental group). *P .05; **P .01; ***P .001.

Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "Eosinophils contribute to innate antiviral immunity and promote clearance of respiratory syncytial virus author" ?

In this paper, the role of eosinophils in immunity against infectious pathogens was investigated, and it was shown that eosINophils contribute to host defense or to the immunopathology observed in response to RSV infection. 

Q2. What is the role of eosinophils in antiviral immunity?

Eosinophil NO production contributes to antiviral immunity from RSVNitric oxide (NO) has been implicated in antiviral host defense and may also be functionally protective through bronchodilatory mechanisms. 

Q3. What is the role of TLRs in the accelerated clearance of RSV?

The immediate response to RSV infection in immunocompetent hosts includes recruitment of proinflammatory granulocytes, which themselves express TLRs. 

Q4. How did eosinophil transfer reduce AHR in RSV-infected?

Eosinophil transfer reduces AHR in RSV-infected miceBecause RSV infection has been associated with AHR, the authors next examined whether eosinophil-mediated viral clearance could suppress RSV-induced AHR. 

Q5. What is the role of eosinophils in promoting antiviral immunity?

Eosinophils directly transferred into the airways have been shown to remain functional and can migrate into the lung and local pulmonary lymph nodes, where they actively participate in immune responses. 

Q6. What is the role of eosinophils in the modulation of immune or?

it is likely that the role ofeosinophils in the modulation of immune or pathologic processes is highly dependent on signals received from the microenvironment and signals that are associated with specific inflammatory responses. 

Q7. What is the role of TLRs in the development of adaptive immune responses?

the authors show that eosinophil-mediated accelerated RSV clearance and attenuated lung dysfunction are dependent on the TIR adaptor molecule MyD88 and the production of NO by NOS-2.TLRs are a conserved family of PRRs that bridge innate pathogen recognition and the development of adaptive (T and B lymphocyte) immune responses. 

Q8. What is the role of eosinophils in the inflammatory process?

In the setting of allergic asthma, where eosinophils are prevalent in the airway mucosa and exacerbations of disease are most frequently caused by viral infections, eosinophils have often been implicated as a causative agent of AHR.49-51 

Q9. What is the effect of RSV infection on the lungs of mice?

RSV infection resulted in an increase in the number of goblet cells secreting mucus into the airways in both hypereosinophilic and WT mice within 24 hours (data not shown). 

Q10. What is the effect of L-NMA on the clearance of RSV in WT mice?

L-NMA significantly delayed the clearance of RSV in WT mice, and completely reversed the advantage conferred by the hypereosinophilic status of IL-5 Tg mice (Figure 5C). 

Q11. How did the authors determine that accelerated virus clearance was due to eosinophils?

To confirm that accelerated virus clearance was due specifically to eosinophils and not the overexpression of IL-5, the authors FACSpurified eosinophils ( 98% pure) from the spleens of hypereosinophilic mice, and performed an adoptive transfer directly into the lungs of WT mice 2 hours before RSV inoculation. 

Q12. How did the authors determine whether eosinophils confer protection from RSV?

To demonstrate that eosinophils confer protection from RSV, the authors used dblGATA mice, whose eosinophil lineage is selectively and severely disrupted. 

Q13. What was the RNA integrity of the eosinophils recovered by FACS?

Eosinophils recovered by FACS (BD Biosciences FACS Vantage Diva) were approximately 99% pure as determined by Giemsa-stained cytospin preparations. 

Q14. How does the mouse show that TLR-7 can recognize RSV?

In the mouse, the authors demonstrate at the protein level that eosinophils express another TLR that can recognize molecular patterns expressed by RSV, namely TLR-7. 

Q15. What did the authors find out about the effect of RSV on eosinophils?

Having demonstrated that RSV induces systemic effects, the authors next determined if antiviral genes were induced in eosinophils in response to infection.