Pereira Lipid antigen presentation in Fabry disease patients

The lysosome is a cellular organelle responsible for the degradation of macromolecules. Lysosomal storage diseases (LSDs) arise from the accumulation of undegraded macromolecules in the lysosome, mainly due to genetic defects in the lysosomal hydrolases. Fabry disease is a LSD caused by mutations in the GLA gene which codifies the enzyme α-Galactosidase A, a lysosomal hydrolase responsible for globotriaosilceramide degradation. The lysosome is also a key player in the process of lipid antigen presentation to T cells. Lipid antigen presentation is mediated by CD1 molecules existent in antigen presenting cells (APCs), which associate with lipid antigens, forming complexes that are able to activate T cells responsive to CD1 molecules (CD1restricted T cells). There are five isoforms of CD1 molecules (a,b,c,d,e), but only four of them (a,b,c,d) present lipid antigens to T cells. The four isoforms have different intracellular trafficking patterns. One of the places where association of lipid antigens with CD1 molecules occurs is the lysosome. Therefore, it was hypothesized that the process of lipid antigen presentation and consequent activation of CD1-restricted T cells is impaired in LSDs. Several mouse models of LSDs, including Fabry disease, were already shown to have reduced frequencies of a specific type of CD1d-restricted T cells (iNKT cells) and decreased capacity of lipid antigen presentation. In humans, previous studies have found no alterations in iNKT cell percentage in patients of two different LSDs: Gaucher and Fabry diseases. Studies assessing the efficiency of lipid antigen presentation in LSD patients are missing. In this study, we analysed the iNKT cells and iNKT cell subsets and the capacity of lipid antigen presentation of Fabry disease patients. We found no differences in percentage of iNKT cells between Fabry disease and control subjects. In humans, iNKT cells can be divided in three subsets that produce different types of cytokines according to CD4 and CD8 expression: iNKT cells expressing only CD4 (CD4) produce Th1 and Th2 cytokines, iNKT cells that do not express both molecules (DN) produce mainly Th1 and iNKT cells that only express CD8 (CD8) produce mostly IFN-γ. In this study, we found a reduction in iNKT CD4 subset in Fabry disease patients when compared to control subjects. In lipid antigen presentation assays, five patients were tested for the capacity of their dendritic cells to present lipid antigens by two CD1 molecules: CD1b and d. We found no alterations in patients’ capacity to present the lipid antigen sulfatide by CD1b. Interestingly, presentation of the lipid antigen GM1 by CD1b was reduced in two patients. Regarding CD1d molecules, two patients had reduced capacity of presenting sulfatide when compared to control subjects. Concluding, we found an imbalance in the iNKT cell subsets in Fabry disease patients that can be associated with an alteration in cytokine profile which might contribute to disease pathology. Lipid antigen presentation assays were for the first time performed in LSDs patients, but more studies are needed to take further conclusions.