Organ Procurement Organizations (OPO) partnering with nPOD to provide research resources are listed at http://www.jdrfnpod.org/our-partners.php. “
“Major histocompatibility complex (MHC) class II molecules present antigenic peptides derived from engulfed exogenous proteins to CD4+ T cells. Exogenous antigens are processed in mature endosomes and lysosomes where acidic proteases reside and peptide-binding to class II alleles is favoured. Hence, maintenance of the microenvironment within these organelles is probably central to efficient MHC class II-mediated antigen presentation. Lysosome-associated PI3K inhibitor membrane

proteins such as LAMP-2 reside in mature endosomes Romidepsin in vitro and lysosomes, yet their role in exogenous antigen presentation

pathways remains untested. In this study, human B cells lacking LAMP-2 were examined for changes in MHC class II-restricted antigen presentation. MHC class II presentation of exogenous antigen and peptides to CD4+ T cells was impaired in the LAMP-2-deficient B cells. Peptide-binding to MHC class II on LAMP-2-deficient B cells was reduced at physiological pH compared with wild-type cells. However, peptide-binding and class II-restricted antigen presentation were restored by incubation of LAMP-2-negative B cells at acidic pH, suggesting that efficient loading of exogenous epitopes by MHC class II molecules is dependent upon LAMP-2 expression in B cells. Interestingly, class II presentation of an epitope derived from an endogenous transmembrane protein was Methamphetamine detected using LAMP-2-deficient B cells. Consequently, LAMP-2 may control the repertoire of peptides displayed by MHC class II molecules on B cells and influence the balance between endogenous and exogenous antigen presentation. Major histocompatibility complex (MHC) class II molecules

present antigenic peptides derived from exogenous proteins to CD4+ T cells.1 These MHC class II proteins are constitutively expressed on the surface of a number of professional antigen-presenting cells (APC) such as dendritic cells, B cells and macrophages. The MHC class II complexes consist of α and β subunits which are first assembled in the endoplasmic reticulum with the chaperone molecule invariant chain (Ii).2,3 The cytoplasmic tail of Ii contains a motif that targets the Ii–MHC class II complexes to endosomal/lysosomal compartments. Here, acidic proteases degrade Ii to a small fragment known as class II-associated invariant chain peptide (CLIP), which remains associated with the MHC class II peptide-binding groove.4,5 Antigens delivered into the endosomal/lysosomal network via receptor-mediated or fluid-phase endocytosis are also exposed to proteases and denaturing reactions, yielding peptide ligands for class II molecules.