|Ph.D Student||Bettman Noam|
|Subject||Monocyte Dysfunction in Gaucher's Disease|
|Department||Department of Medicine||Supervisors||Dr. Irit Avivi|
|Dr. Hanna Rosenbaum|
|Dr. Tamar Katz|
|Full Thesis text|
Gaucher’s disease (GD) is the most prevalent lysosomal storage disorder. The disease, caused by a marked deficiency in β-glucocerebrosidase function, is characterized by low blood counts, organomegaly, various bone manifestations and immune-related alterations.
Monocytes are myeloid-linage immune cells that migrate out of the bone-marrow and replenish peripheral tissues, monitoring it for pathogens. These cells also activate and regulate innate and adaptive immune functions and differentiate into tissue resident macrophages and dendritic cells (DCs). As monocytes exert a most prominent β-glucocerebrosidase function, its functional deficiency in GD might impair monocyte function and cause some of the disease immune alterations. The aim of this study was to test monocyte functions in Gaucher’s patients and to clarify the mechanisms of their dysfunction.
Anti-CD14 (a monocyte marker) staining of patients’ and healthy volunteers’ (HVs) blood samples, showed patients to have significantly fewer monocytes in their blood (9% vs. 13.5%; p<0.05). In vitro migration tests towards stromal-cell derived factor 1α (SDF1α; 0.5μg/ml & 1μg/ml) revealed that patients-derived monocyte migration is significantly impaired (6.3% and 9% vs. 14% and 21.8% in HVs, respectively; p<0.05 for both concentrations). Similar amounts of SDF1α cognate receptor [CXC-motif chemokine receptor (CXCR) 4] mRNA transcripts were found in patients’ and HVs’ monocytes. Nevertheless, the surfaced CXCR4 expression was lower in patients’ monocytes and higher within the cells, while HVs-derived cells had high extracellular and low intracellular CXCR4 expression (43.9% and 56.4% vs. 60.3% and 32.2%, respectively; p<0.01). The different CXCR4 distribution might result from elevated SDF1α levels found in patients’ serum (2603pg/ml vs. 2039pg/ml in HVs’; p<0.01), causing its internalization. Similar SDF1α-CXCR4 binding, CXCR4 function and CXCR7 (SDF1α-scavenging receptor) expression were recorded in patients and HVs, precluding these mechanisms contribution in affecting GD patients-derived SDF1α-dependent migration. HVs’ monocyte migration and CXCR4 expression were not changed upon β-glucocerebrosidase inhibition.
Antigen uptake test revealed an inferior capacity of GD-derived monocytes to engulf antigens (37.8% vs. 57.9%; p<0.05), and patients also showed decreased numbers of several DCs precursors. GD monocyte-derived DCs showed impaired function, both as immature DCs (antigen uptake) and mature DCs (T cell viability and interferon-γ secretion). Interestingly, patients receiving enzyme replacement therapy had increased amounts of monocytes and DCs precursors, while serum substitution improved DCs antigen uptake capacity and T cells interferon-γ secretion.
Our results indicate an impaired monocyte function in GD patients, which relates to patients’ serum (the functional impairments) and β-glucocerebrosidase deficiency (the quantitative impairments).