10 The resulting peptide–MHC class II complexes are ultimately trafficked to the cell surface for immune surveillance by CD4+ T cells. Mature endosomes and lysosomes play critical roles in routine intracellular processes such as protein degradation as well as more specialized functions related to selleck products antigen presentation by MHC class II molecules.10,11 These morphologically heterogeneous organelles are distinguishable from other intracellular compartments in most cells by the presence of mature acid-dependent hydrolases and lysosome-associated
membrane proteins such as LAMP-1 and LAMP-2.12 LAMP-1 and LAMP-2 are members of a family of highly glycosylated transmembrane proteins primarily located in mature endosomes and lysosomes.13 A deficiency in LAMP-2 is linked with the development of an X-linked lysosomal storage disorder known as Danon disease;14 genetic analysis of patients with this disorder demonstrated several mutations in the LAMP-2 gene causing protein truncations and an absence of protein expression in patient tissues.15 Danon disease patients display an accumulation of dense and translucent vacuoles, possibly autophagosomes, in the cells of multiple tissues.15 Additionally,
studies with LAMP-2 knockout mice reveal Napabucasin supplier an accumulation of autophagic vacuoles in many tissues possibly because of impaired lysosomal trafficking.16,17
The LAMP-2 gene encoded on the X-chromosome gives rise to several alternative transcripts encoding protein isoforms that differ primarily in their cytoplasmic tail domains.18 Among these isoforms, LAMP-2A and -2B proteins are ubiquitously expressed in most tissues including lymphocytes.19 LAMP-2A serves as the lysosomal receptor for chaperone-mediated autophagy, a pathway promoting the transport of specific cytosolic proteins into lysosomes via a molecular chaperone/receptor complex.20–22 Over-expression of LAMP-2A or hsc70, a chaperone protein that co-operates with LAMP-2A in chaperone-mediated autophagy, enhanced the MHC class II-restricted presentation of two cytoplasmic autoantigens in human B cells, hence establishing a role for LAMP-2 in cytoplasmic antigen presentation.19 Remarkably, Endonuclease a partial decrease in total LAMP-2 expression in human B cells reduced not only cytoplasmic antigen presentation but also exogenous antigen presentation by MHC class II molecules.19 Studies here address how the complete loss of LAMP-2 in human B cells modulates epitope selection and display in the context of MHC class II. In the absence of LAMP-2, human B cells displayed a reduced capacity for MHC class II-restricted presentation of exogenous antigen and peptides but maintained the presentation of epitopes from an endogenous transmembrane protein.