Multi-Modal Characterization of Monocytes in Idiopathic Pulmonary Fibrosis Reveals a Primed Type I Interferon Immune Phenotype.

Emily Fraser,Yuejuan Zheng,Rachel E Rigby,Laura Denney,Alison Simmons,Agne Antanaviciute,Karl Blirando,Valentina Iotchkova,Neil Ashley,Emmanouela Repapi,Ling-Pei Ho,Stephen Taylor,Colin Clelland,Chaitanya Vuppusetty,Clare S Hardman,Rachel Benamore,Jan Rehwinkel,Victoria St Noble,Rachel Hoyles,Nasullah Khalid Alham ,Joseph M Rastrick

doi:10.3389/fimmu.2021.623430

Abstract

Idiopathic pulmonary fibrosis (IPF) is the most severe form of chronic lung fibrosis. Circulating monocytes have been implicated in immune pathology in IPF but their phenotype is unknown. In this work, we determined the immune phenotype of monocytes in IPF using multi-colour flow cytometry, RNA sequencing and corresponding serum factors, and mapped the main findings to amount of lung fibrosis and single cell transcriptomic landscape of myeloid cells in IPF lungs. We show that monocytes from IPF patients displayed increased expression of CD64 (FcγR1) which correlated with amount of lung fibrosis, and an amplified type I IFN response ex vivo. These were accompanied by markedly raised CSF-1 levels, IL-6, and CCL-2 in serum of IPF patients. Interrogation of single cell transcriptomic data from human IPF lungs revealed increased proportion of CD64hi monocytes and “transitional macrophages” with higher expression of CCL-2 and type I IFN genes. Our study shows that monocytes in IPF patients are phenotypically distinct from age-matched controls, with a primed type I IFN pathway that may contribute to driving chronic inflammation and fibrosis. These findings strengthen the potential role of monocytes in the pathogenesis of IPF.

Highlights

Idiopathic pulmonary fibrosis (IPF) is the most severe form of chronic fibrotic lung disease [1]
Data were analyzed for all IPF patients (n=37) vs age-matched healthy controls (HC) (n=28), and after dividing patients into those on Pirfenidone treatment compared to those without
Monocyte levels correlated positively with the extent of fibrosis in the patients’ lungs, as measured on high resolution computed tomographic (CT) scans (Figure 1C), but not significantly with lung function (Supplementary Figures 1C, D). This suggests that monocyte levels are more closely associated with fibrosis, since lung function abnormalities can be contributed by other factors like cardiac dysfunction, emphysema, and pulmonary hypertension

Summary

Introduction

Idiopathic pulmonary fibrosis (IPF) is the most severe form of chronic fibrotic lung disease [1]. The fibrosis is progressive, and median survival is only five years from diagnosis. Repeated but minor insults to the alveolar epithelium are thought to lead to a disproportionate repair response by fibroblasts and other mesenchymal cells [2]. Research has focused more intensely on the abnormal repair response, and less on the drivers of chronic fibrosis. A recent study suggest that monocytes may be linked to progression of fibrosis in IPF, since increased levels in IPF patients were correlated with poorer survival [3]. No further immune phenotyping data on these monocytes were available to guide further mechanistic studies

Methods

Results

Conclusion