Characterization of the role of CCRL2 in lung and intestine immune surveillance

The C-C chemokine receptor-like 2 (CCRL2) belongs to the class-A GPCR receptor and is related to the atypical chemokine receptors (ACKRs) family. It regulates leukocyte migration by acting as a Chemerin-presenting molecule, as well as forming heterodimers with other chemokine receptors. CCRL2 is expressed by a large variety of leukocytes and barrier cells and controls the inflammatory response in different pathological settings. For instance, in lung cancer CCRL2 is required for NK cell recruitment and immune surveillance. This thesis explored the multifaceted role of CCRL2 in the immune regulation of the lung and intestine. Firstly, we investigated the correlation between CCRL2 variants and the severity of COVID-19. Five CCRL2 missense polymorphisms common among Europeans were selected and investigated in the meta-analysis of the COVID-19 host genetics initiative (COVID19 HGI) and in the Italian cohort referring to the Humanitas Clinical and Research Center (Rozzano, Milan). We have identified an association between the p.I243V variant and severe respiratory COVID-19 in Europeans. Functional assessments revealed that these variants do not affect CCRL2 membrane expression or Chemerin binding. Additionally, we identify CCRL2 eQTLs specific to neutrophils, linked to COVID-19 associated SNPs, suggesting a targeted influence on neutrophils. The study also delved into CCRL2 involvement in the regulation of intestinal inflammation and tumorigenesis. Genetic ablation of Ccrl2 in murine models of DSS-induced colitis and AOM/DSS-induced colon cancer revealed a more severe inflammatory phenotype, a finding corroborated in VillinCreHe-CCRL2f/f mice, emphasizing CCRL2 role in regulating the intestinal epithelium. Furthermore, we have observed an increased permeability in intestinal organoids from Ccrl2 KO mice, suggesting a role for this receptor in maintaining intestinal barrier integrity. The absence of Ccrl2 also modulated the expression and release of certain pro-inflammatory cytokines and chemokines by intestinal organoids treated with TNF-α and IFN-. In conclusion, this study highlighted the impact of CCRL2 in neutrophil-mediated responses and COVID-19 severity. CCRL2 also plays a role in the regulation of intestinal epithelium functions and permeability, especially during inflammatory responses. Collectively, these results contribute to a more comprehensive understanding of CCRL2 functions and its potential implications in the immune surveillance of the lung and intestine.