IL-17E (IL-25) and IL-17RB promote respiratory syncytial virus-induced pulmonary disease

Abstract

One of the most severe pathologic responses of RSV infection is associated with overproduction of cytokines and inflammation, leading to mucus hypersecretion. This study investigated the role of IL-25 in the development of RSV-associated immunopathology. IL-25 and its receptor IL-17RB were increased following RSV infection, and IL-25 blockade using neutralizing antibodies reduced RSV-associated pathology, AHR, and type 2 cytokine production. Likewise, IL-17RB^-/- mice demonstrated a modified inflammatory response during RSV infection characterized by decreased Th2 and increased Th17 cytokine production. Additionally, the IL-17RB^-/- mice demonstrated significantly reduced inflammation and cytokine production in a model of RSV-driven asthma exacerbation. These results indicate that IL-25 regulates the inflammatory response to RSV infection and that its inhibition may enable a reduction in the severity of RSV-associated pulmonary inflammation, including during viral-induced asthma exacerbation.

Keywords: Th2; cytokines; mucus.

Figure 1.. Expression of IL-25 and its receptor IL-17RB in lungs of RSV-infected Balb/c mice is associated with cytokine responses and T cell cytokine expression.

(A) IL-25 and (B) IL-17RB mRNA expression are both up-regulated during RSV infection in the lungs and (C) correlates to increased expression of RSV-induced cytokines, IFN-γ, and IL-13. (D) Quantitative PCR analysis of RSV-restimulated LN cells from 8-day-infected animals, with or without IL-25. *P<0.05. (E) Flow cytometry of reactivated T cells from RSV-infected mice demonstrates that CD4⁺ IL-17RB⁺ cells (blue line) preferentially express increased transcription factors, GATA3 and T-bet, whereas CD8⁺ T cells did not. Data represents mean ± se from five mice.

Figure 2.. Blockade of IL-25 during RSV infection in Balb/c mice attenuates goblet cell-associated pathology and mucus production.

Naive Balb/c mice were infected with RSV (1×10⁵ PFU/mouse), treated with control or anti-IL-25 polyclonal rabbit anti-mouse antibody on Days 0, 2, 4, and 6, and harvested on Day 8. (A) AHR and (B) mucus-associated pulmonary gob5 expression after 8 days of infection. Cab, control antibody; Ctrl, control. (C) Histologic assessment of PAS-stained lung sections illustrates a reduction in mucus-stained airways (pink). (D) Flow cytometric assessment of individual immune cell populations in lungs of infected mice depicts no reduction in cell accumulation. Mono, Monocyte; Mϕ, macrophage; cDC, conventional dendritic cell; Macs, macrophages. (E) RSV-restimulated lung draining LN culture supernatants were assayed by Bioplex for cytokine levels. Data represent mean ± se from five mice/group. *P < 0.05 and is representative of three repeat studies.

Figure 3.. Infection of IL-17RB^−/− C5BL/6 mice demonstrates a reduction in disease pathology and alteration of cytokine responses.

(A) Examination of lung pathology, 8 days post-RSV infection, demonstrated a reduction in inflammation and PAS-stained mucus production. (B) Quantitative PCR of RSV G protein in the lungs of 8-day-infected mice. The cytokine mRNA expression in the lungs (C) and protein in RSV-rechallenge draining LN cells (D) displayed a different profile in IL-17RB^−/− mice. (E) The mRNA expression of GATA3 and T-bet transcription factors was reduced in IL-17RB^−/− mice. Data represent mean ± se from five mice/group and are representative of three repeat studies. *P < 0.05.

Figure 4.. RSV-induced exacerbation of allergic airway responses is attenuated in IL-17RB^−/− C57BL/6 mice.

Allergic mice were infected with RSV and challenge two times with allergen (see Materials and Methods) to expose animals simultaneously to the stimuli. (A) Flow cytometry analyses indicated that the primary IL-17RB⁺ cell population that was increased was granulocytes. (B) Analysis of all leukocyte subsets indicated no significant change in any individual population. (C) Histological examination reflected the flow cytometry analysis in (B) indicating similar inflammatory cell accumulation in IL-17RB^−/− mice; however, a reduced intensity in the PAS-postitive staining was evident in the RSV-exacerbated animals compared with WT. Arrows indicate PAS-stained goblet cells. (D) Quantitative PCR analysis of whole lung mRNA indicated that RSV-exacerbated IL-17RB^−/− animals demonstrated a reduction in IL-13 and gob5 mucus gene expression. Muc5AC, Mucin 5AC. Data represent mean ± se from five mice/group.*P < 0.05; **P<0.01. This study was repeated twice with similar results.