Peripheral Blood Dendritic Cell Subsets of Patients with Type I Gaucher’s Disease Are Decreased in Number but Functionally Normal.

Introduction - Aims: Gaucher’s disease is a lysosomal storage disorder, in which undigested glucocerebroside is deposited in the cytoplasm of mature macrophages, which accumulate in the bone marrow and the reticuloendothelial system. Dendritic cells (DC) are bone-marrow-derived leukocytes, originating from the pluripotent hematopoietic stem cell, via different developmental pathways, related to myeloid or lymphoid lineage. They belong to the monocyte-macrophage system and are specialized for the uptake, processing, transport and presentation of antigens to T-cells. There is no information about the functional capacity of DC among patients with lysosomal storage disorders. We therefore, investigated in the status of blood DC precursor populations as well as the potential of bone marrow (BM)-derived progenitor cells to produce mature DC in patients with Gaucher’s disease.

Patients and methods: Samples of heparinized PB and/or BM were obtained from 11 patients with type I Gaucher’s disease and 15 healthy volunteers, after informed consent. Nine patients were studied before any kind of treatment and the remaining 2 had been treated with imiglucerase 40 IU/kg of body weight at monthly intervals, for 24 months. All patients were anemic and thrombocytopenic, but none had severe bone disease. The myeloid DC (MDC) precursors and the more specialized cell type, the plasmacytoid DC (PDC) were detected in the peripheral blood by flow cytometry, based on the expression of immunoglobulin-like transcript (ILT)-3, together with lineage-specific markers CD3, CD56, CD14, CD16 and CD11c. The potential of PB monocytes, as DC precursors, and of BM CD34⁺ progenitors to differentiate into mature DC was studied in culture systems. Generated mature DC were immunophenotyped, and tested for their dextran-endocytic capacity, as well as for their stimulatory activity against allogeneic T-cells in mixed cultures.

Results: Both, MDC and PDC from peripheral blood of patients with Gaucher’s disease were decreased, when compared to controls (MDC 0.20±0.11% vs. 0.33±0.14%, p=0.02 and PDC 0.19±0.15% vs. 0.40±0.17%, p=0.005). The yield of monocyte-derived DC (MoDC), obtained after GM-CSF and IL-4 stimulation, was lower than in controls (4.9±3.5% vs. 8.2±4%, p=0.012), although no difference was found in the percentage of monocytes initiating the culture. However, the immunophenotype profile, estimated by CD1a, CD40, CD54, CD80, CD83, and HLA-DR expression, the endocytic capacity, and the allo-stimulatory capacity of immature, and of TNFα- or LPS-stimulated mature MoDC were similar to those obtained by healthy controls. In addition, BM-derived CD34⁺ cells, differentiated in the presence of GM-CSF, SCF, TNF-α and IL-4 into mature DC, did not differ in number, phenotype and allo-stimulatory activity from those of controls.

Conclusive remarks: Our findings suggest that in patients with type I Gaucher’s disease, mainly quantitative defects of DC system are present, demonstrated by decreased circulating DC precursors of both, MDC and PDC type. Moreover, with the exception of decreased MoDC production, no additional functional/qualitative defects of both, CD34-DC and MoDC, concerning their membrane immunophenotype, endocytic and allostimulatory capacity were detected.