Galectin-3 enhances monocyte-derived macrophage efferocytosis of apoptotic granulocytes in asthma

BackgroundGalectin-3 is a 32kDa protein secreted by macrophages involved in processes such as cell activation, chemotaxis and phagocytosis. Galectin-3 has previously been shown to improve the ability of airway macrophages to ingest apoptotic cells (efferocytosis) in chronic obstructive pulmonary disease (COPD) and may be of interest in non-eosinophilic asthma (NEA) which is also characterised by impaired efferocytosis. It was hypothesised that the addition of exogenous galectin-3 to monocyte-derived macrophages (MDMs) derived from donors with NEA would enhance their ability to engulf apoptotic granulocytes.MethodsEligible non-smoking adults with asthma (n=19), including 7 with NEA and healthy controls (n=10) underwent a clinical assessment, venepuncture and sputum induction. MDMs were co-cultured with apoptotic granulocytes isolated from healthy donors with or without exogenous recombinant galectin-3 (50g/mL) and efferocytosis was assessed by flow cytometry. Galectin-3 expression and localisation in MDMs was visualised by immunofluorescence staining and fluorescence microscopy. Galectin-3, interleukin (IL)-6 and CXCL8 secretion were measured in cell culture supernatants by ELISA and cytometric bead array.ResultsBaseline efferocytosis (mean (standard deviation)) was lower in participants with asthma (33.2 (+/- 17.7)%) compared with healthy controls (45.3 (+/- 15.9)%; p=0.081). Efferocytosis did not differ between the participants with eosinophilic asthma (EA) (31.4 (+/- 19.2)%) and NEA (28.7 (+/- 21.5)%; p=0.748). Addition of galectin-3 significantly improved efferocytosis in asthma, particularly in NEA (37.8 (+/- 18.1)%) compared with baseline (30.4 (+/- 19.7)%; p=0.012). Efferocytosis was not associated with any of the clinical outcomes but was negatively correlated with sputum macrophage numbers (Spearman r=-0.671; p=0.017). Galectin-3 was diffusely distributed in most MDMs but formed punctate structures in 5% of MDMs. MDM galectin-3 secretion was lower in asthma (9.99 (2.67, 15.48) ng/mL) compared with the healthy controls (20.72 (11.28, 27.89) ng/mL; p=0.044) while IL-6 and CXCL8 levels were similar.Conclusions p id=Par4 Galectin-3 modulates macrophage function in asthma, indicating a potential role for galectin-3 to reverse impaired efferocytosis in NEA.