A narrative review of chemokine receptors CXCR1 and CXCR2 and their role in acute respiratory distress syndrome.

Acute respiratory distress syndrome (ARDS) is a severe form of acute respiratory failure characterised by extensive inflammatory injury to the alveolocapillary barrier leading to alveolar oedema, impaired gas exchange and, ultimately, hypoxaemia necessitating the use of supplemental oxygen combined with some degree of positive airway pressure. Although much heterogeneity exists regarding the aetiology, localisation and endotypic characterisation of ARDS, what remains largely undisputed is the role of the innate immune system, and in particular of neutrophils, in precipitating and propagating lung injury. Activated neutrophils, recruited to the lung through chemokine gradients, promote injury by releasing oxidants, proteases and neutrophil extracellular traps, which ultimately cause platelet aggregation, microvascular thrombosis and cellular death. Among various neutrophilic chemoattractants, interleukin-8/C-X-C motif ligand 8 and related chemokines, collectively called ELR+ chemokines, acting on neutrophils through the G protein-coupled receptors CXCR1 and CXCR2, are pivotal in orchestrating the neutrophil activation status and chemotaxis in the inflamed lung. This allows efficient elimination of infectious agents while at the same time minimising collateral damage to host tissue. Therefore, understanding how CXCR1 and CXCR2 receptors are regulated is important if we hope to effectively target them for therapeutic use in ARDS. In the following narrative review, we provide an overview of the role of ELR+ chemokines in acute lung injury (ALI) and ARDS, we summarise the relevant regulatory pathways of their cognisant receptors CXCR1/2 and highlight current preclinical and clinical evidence on the therapeutic role of CXCR1 and CXCR2 inhibition in animal models of ALI, as well as in ARDS patients.