The TLR5 Agonist Flagellin Shapes Phenotypical and Functional Activation of Lung Mucosal Antigen Presenting Cells in Neonatal Mice.

Pankaj Sharma,David J Dowling,Ofer Levy

doi:10.3389/fimmu.2020.00171

Pankaj Sharma, David J Dowling + Show 1 more

Open Access

https://doi.org/10.3389/fimmu.2020.00171

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Abstract

Intranasal mucosal vaccines are an attractive approach to induce protective mucosal immune responses. Activation of lung antigen presenting cells (APCs), a phenotypically and functionally heterogeneous cell population located at distinct mucosal sites, may be key to the immunogenicity of such vaccines. Understanding responsiveness of newborn lung APCs to adjuvants may the inform design of efficacious intranasal vaccines for early life, when most infections occur. Here, we characterized and phenotyped APCs from neonatal (7 days of life) and adult (6–8 weeks of age) mice. Neonatal mice demonstrated a relatively high abundance of alveolar macrophages (AMs), with lower percentages of plasmacytoid dendritic cells (pDCs), CD103+ (cDC1), and CD11b+ (cDC2) DCs. Furthermore, neonatal CD103+ and CD11b+ DC subsets demonstrated a significantly lower expression of maturation markers (CD40, CD80, and CD86) as compared to adult mice. Upon stimulation of lung APC subsets with a panel of pattern recognition receptor (PRR) agonists, including those engaging TLRs or STING, CD11c+ enriched cells from neonatal and adult mice lungs demonstrated distinct maturation profiles. Of the agonists tested, the TLR5 ligand, flagellin, was most effective at activating neonatal lung APCs, inducing significantly higher expression of maturation markers on CD103+ (cDC1) and CD11b+ (cDC2) subsets. Intranasal administration of flagellin induced a distinct migration of CD103+ and CD11b+ DC subsets to the mediastinal lymph nodes (mLNs) of neonatal mice. Overall, these findings highlight age-specific differences in the maturation and responsiveness of lung APC subsets to different PRR agonists. The unique efficacy of flagellin in enhancing lung APC activity suggests that it may serve as an effective adjuvant for early life mucosal vaccines.

Highlights

The persistently high global burden of infections in the very young provides a compelling rationale for developing additional safe and effective early life vaccines [1]
By using the combination of different surface markers and a hierarchal gating strategy, we identified alveolar macrophages (AMs), moDCs, CD103+ DCs, CD11b+ DCs, and plasmacytoid DCs (pDCs) (Figure 2A)
While the percentage of Ly6C+ cells was significantly higher in neonatal vs. adult mice (Figure 2B), and AMs and moDCs subsets were similar between both age groups, neonates demonstrated a significanly lower percentage of lung DC subsets CD103+ DCs (n = 12, P < 0.001), CD11b+ DCs (P < 0.001), and pDCs (P < 0.05) (Figure 2C)

Summary

Introduction

The persistently high global burden of infections in the very young provides a compelling rationale for developing additional safe and effective early life vaccines [1]. Viral infections including respiratory syncytial virus (RSV) and influenza virus are often more severe and/or prolonged in early life as compared to adult life [3]. Parenteral vaccines, such as those delivered intramuscularly, are Flagellin Activates Neonatal Lung APCs often poor inducers of protective immunity at mucosal surfaces [4]. Mucosal administration of antigen may drive a more effective mucosal response to respiratory infections [10, 11], potentially reflecting activation of antigen-specific secretory IgA responses and development of lung resident memory T cells [12,13,14]

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