B-Cell Activating Factor secreted by neutrophils is a critical player in lung inflammation to cigarette smoke exposure

S Huot-Marchand,A Gombault,M Nascimento,C Panek,F Savigny,P Schneider,M Le Bert,N Riteau,B Ryffel,V Quesniaux,I Couillin

doi:10.1016/j.rmr.2021.02.034

Abstract

B cell activating factor (BAFF) is a TNF family cytokine mainly produced by adaptive immune cells in particular B and T lymphocytes. Depending on the context, innate immune cells can also produce BAFF. First of all, BAFF was known to play an important role in the maturation and survival of B lymphocytes in humoral immune response. Recent data indicate that BAFF may also participate in the regulation of innate immune responses and in the pathophysiology of pulmonary diseases. In models of mice chronically exposed to cigarette smoke (CS), BAFF plays a major role in the generation of pulmonary antinuclear antibodies and tertiary lymphoid follicles. However, the implication of BAFF in the development of innate immunity to cigarette smoking remains unknown. Wild-type or BAFF deficient mice were exposed to 3R4F cigarette smoke 3 times a day for 4 days. Mice were treated or not with mouse anti-GR1 or recombinant mouse BAFF during CS exposure. Broncho-alveolar lavage fluids (BALF) were done and cell infiltration was determined. Different cytokines and chemokines were measured in BALF and lung homogenates. Immunostaining on cytospin were done. Bone marrow derived neutrophils (BMDN) and Murine tracheal epithelial cells (MTEC) were stimulated in vitro by CSE (Cigarette Smoke Extract). Cell viability and BAFF levels were determined. Acute CS exposure promotes BAFF expression in airway recruited neutrophils. Immunostaining analysis revealed that neutrophils are the major source of BAFF. We confirmed in vitro that neutrophils secrete BAFF in response to CSE stimulation. Neutrophil depletion partially decreases BAFF expression in lung tissue and bronchoalveolar space suggesting additional sources of BAFF. Importantly, BAFF deficient mice displayed decreased airway neutrophil recruiting chemokines and neutrophil influx while the addition of exogenous BAFF significantly enhanced this CS-induced neutrophilic inflammation. These results demonstrate that BAFF is a key pro-inflammatory cytokine and that innate immune cells in particular neutrophils, are an unconsidered source of BAFF in early stages of CS-induced innate immunity.

Highlights

Inflammatory lung diseases represent a major public health problem
wild type mice (WT) mice exposed to cigarette smoke (CS) presented significant increase in the number of total cells recruited into the bronchoalveolar lavage (BAL) (Figure 1A) and in particular neutrophils (Figure 1B) and macrophages (Figure 1C), as well as enhanced myeloperoxidase (MPO) levels (Figure 1D) in BAL fluid (BALF) which correlates with neutrophil recruitment
BAL cells immunostaining assay employing B cell activating factor (BAFF) specific antibody indicates that airways recruited neutrophils, identified by their multi-lobulated nucleus stained with DAPI, strongly express BAFF in response to CS (Figures 1H,I)

Summary

Introduction

Inflammatory lung diseases represent a major public health problem Their incidence is constantly increasing and the predictions of the World Health Organization (WHO) are at least pessimistic over the 20–30 years, reflecting recent changes in our society and the associated consequences on air quality and social behavior. A sustained cellular inflammation characterized by airway neutrophilic recruitment is commonly correlated with bad prognosis in chronic lung inflammation and COPD exacerbations elicited by a bacterial or viral infection [2]. This strong inflammatory response is associated with impaired bacterial clearance due to ineffective neutrophils which do not prevent the occurrence of infection-driven exacerbations [1]. The transition between proinflammatory and immunosuppressive neutrophils is highly dynamic and neutrophil plasticity may influence immune responses to environmental stress such as CS exposure [6]

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Results

Conclusion