Upregulation of leukocyte immunoglobulin-like receptor B4 on interstitial macrophages in COPD; their possible protective role against emphysema formation

Abstract

Background Leukocyte immunoglobulin-like receptor B4 (LILRB4) is one of the inhibitory receptors in various types of immune cells including macrophages. Previous reports suggested that LILRB4 could be involved in a negative feedback system to prevent excessive inflammatory responses. However, its role has been unclear in chronic obstructive pulmonary disease (COPD), in which macrophages play a crucial role in the pathogenesis. In this study, we aimed to examine the changes of LILRB4 on macrophages both in the lung specimens of COPD patients and the lungs of a mouse emphysema model. We then tried to compare the differences in both inflammation and emphysematous changes of the model between wild-type and LILRB4-deficient mice in order to elucidate the role of LILRB4 in the pathogenesis of COPD. Methods We prepared single-cell suspensions of resected lung specimens of never-smokers (n = 21), non-COPD smokers (n = 16), and COPD patients (n = 14). The identification of LILRB4-expressing cells and the level of LILRB4 expression were evaluated by flow cytometry. We analyzed the relationships between the LILRB4 expression and clinical characteristics including respiratory function. In the experiments using an elastase-induced mouse model of emphysema, we also analyzed the LILRB4 expression on lung macrophages. We compared inflammatory cell accumulation and emphysematous changes induced by elastase instillation between wild-type and LILRB4-deficient mice. Results The levels of surface expression of LILRB4 are relatively high on monocyte linage cells including macrophages in the human lungs. The percentage of LILRB4+ cells in lung interstitial macrophages was increased in COPD patients compared to non-COPD smokers (p = 0.018) and correlated with the severity of emphysematous lesions detected by CT scan (rs = 0.559, p < 0.001), whereas the amount of smoking showed no correlation with LILRB4 expression. Increased LILRB4 on interstitial macrophages was also observed in elastase-treated mice (p = 0.008). LILRB4-deficient mice showed severer emphysematous lesions with increased MMP-12 expression in the model. Conclusions LILRB4 on interstitial macrophages was upregulated both in human COPD lungs and in a mouse model of emphysema. This upregulated LILRB4 may have a protective effect against emphysema formation, possibly through decreasing MMP-12 expression in the lungs.

Differential effects of sugar and fat on adipose tissue inflammation

“… 29 , 30 LILRB4, leukocyte immunoglobulin-like receptor B4, is an inhibitory receptor on macrophages that prevents excessive inflammation. 31 LGALS3 (galectin-3) is a galactose-specific lectin that regulates macrophage adhesion and migration. Loss of LGALS3 results in increased expression of proinflammatory genes.…”

LILRB4 Checkpoint for Immunotherapy: Structure, Mechanism and Disease Targets

“…LILRB4 was found to be upregulated on interstitial macrophages in human chronic obstructive pulmonary disease and mouse emphysema models. Upregulation of LILRB4 may exert a protective effect against emphysema formation by decreasing the expression of matrix metalloproteinase MMP-12 in the lungs [125]. Moreover, in other inflammatory lung conditions, such as acute lung injury, a lack of LILRB4 expression would exacerbate acute lung injury through NF-κB signaling in bone marrow-derived macrophages [126].…”

Research progress of B subfamily of leucocyte immunoglobulin‐like receptors in inflammation

“…Increased MMP‐12 production led to more severe emphysema lesions. However, up‐regulation of LILRB4 protected against chronic obstructive disease lung disease (Mitsune et al., 2021). Patel et al.…”

“…Increased MMP-12 production led to more severe emphysema lesions. However, up-regulation of LILRB4 protected against chronic obstructive disease lung disease (Mitsune et al, 2021). Patel et al (2021) found that six proteins (IL-NF-6, CKAP4, Gal-9, IL-1ra, LILRB4 and PD-L1) were associated with the severity of COVID-19 and were proportional to disease symptom severity.…”