Lymphocytes and dendritic cells in mucopolysaccharidosis type VI patients

Lysosomal storage diseases (LSD) are a group of rare hereditary metabolic disorders caused by accumulation of undegraded molecules in the lysosome, mainly due to the impairment of the function of lysosomal enzymes. Mucopolysaccharidoses are LSDs characterized by the accumulation of glycosaminoglycans. The focus of this work is Mucopolysaccharidosis type VI (MPS VI), which is a disorder caused by mutations in the gene encoding the ASB enzyme (ARSB). In this disease there is accumulation of the glycosaminoglycan dermatan sulfate. The lysosome is an important organelle in the presentation of lipid antigen to T cells. Invariant natural killer T cells (iNKT) are the most studied lipid specific T cells and are well known by their immunoregulatory properties. In this work seven MPS VI patients from Metabolic Diseases Unit, São João Hospital and seven control subjects from Blood bank, São João Hospital were analyzed. All patients analyzed were under Enzyme Replacement Therapy. For this study B, T and iNKT peripheral blood lymphocytes were analyzed by flow cytometry. For three of the patients dendritic cells (DCs) were differentiated from monocytes and their phenotype was analyzed by flow cytometry. For lipid antigen presentation assays three patients were analyzed. In MPS VI patients we found no alterations in the percentage of the T and iNKT cells and in their subsets according to CD4 and CD8 expression. These parameters have been previously analysed for other LSDs in our laboratory and imbalances in the iNKT cell subsets were found (Cátia Pereira et al. 2013, Molecular Genetics and Metabolism and unpublished results). The results obtained with the MPS VI patients highlight the fact that lysosome dysfunction per se is not sufficient to induce iNKT subset alterations. For B lymphocytes we found an increase in the percentage of these cells in MPS VI patients when compared with control subjects. For dendritic cells phenotype three patients were analyzed. For two of them we found a decrease in the expression of CD1a, CD11c and HLA-DR (MHC-class II). In lipid antigen presentation assays, three patients were tested for the capacity of their dendritic cells to present lipid antigens by the CD1b molecule. We found no alterations in patients’ capacity to present the lipid antigen GM1 by the CD1b molecule. At the moment we are actively recruiting more patients and also collecting clinical data in order to perform association studies.