Full length cDNA of rat RT1.DMa and RT1.DMb and expression of RT1.DM genes in dendritic and Langerhans cells

Assembly, Intracellular Transport, and Release of MHC Class II Peptide Receptors

MHC class II molecules play a pivotal role for the induction and maintenance of immune responses against pathogens, but are also implicated in pathological conditions like autoimmune diseases or rejection of transplanted organs. Human antigen-presenting cells express three human leukocyte antigen (HLA) class II isotypes (DR, DP, and DQ), which are, with the exception of DRα, composed of highly polymorphic α and β subunits. The combination of α- and β-chains results in a multitude of MHC-II αβ-heterodimers of the same isotype, but also isotype-mixed MHC class II molecules have been identified. Invariant chain chaperones the assembly of MHC-II molecules within the endoplasmatic reticulum and also facilitates the intracellular transport to MHC class II loading compartments (MIICs). MHC-II molecules are loaded with antigenic peptides and shuttled to the cell surface for inspection by CD4 T-cells. Alternatively, class-II molecules enriched on intraluminal vesicles can be released via exosomes into the extracellular space. Since some of the αβ-combinations may yield mismatched nonfunctional heterodimers, it is not entirely clear which type of HLA class II peptide receptors are transported to MIICs and found on the cell surface of antigen-presenting cells. We present techniques to inspect assembly, intracellular transport, cell surface expression, and exosomal release of MHC class II heterodimers.

Assembly of matched alpha/beta subunits to HLA class II peptide receptors

Human antigen presenting cells express three human leukocyte antigen (HLA) class II isotypes (DR, DP, and DQ), which are composed of polymorphic α and β subunits. The combination of polymorphic α- and β-chains results in cis (encoded on the same chromosome) or trans (encoded on different chromosomes) combinations. Since some of the α-β combinations may yield mismatched non-functional α-β heterodimers, it is not entirely clear which type of HLA class II peptide receptors are found on the cell surface of antigen presenting cells. We have developed a combination of biochemical techniques for inspection of the assembly and intracellular transport of isotype matched and mismatched class II heterodimers.

Novel antibody tags from the rat lysosomal protein RT1.DM for immunodetection of recombinant proteins

Previously, two mouse monoclonal antibodies (12B8 and 6D4) were raised against the alpha- and beta-subunits of the rat non-classical MHC class-II heterodimer RT1.DM. Here, I describe the epitope mapping of mAb 12B8 to amino acids alpha3-14 (EASPQAWWDESQ) and mAb 6D4 to amino acids beta35-44 (WDPEEGQIVP). Epitope mapping was conducted by preparing fusion proteins between the alpha and beta chain of RT1.DM for Western detection with mAb 12B8 and 6D4. By mutating non-conserved amino acids of the human orthologue of RT1.DM, the rat epitopes were introduced, thereby making the alpha and beta polypeptides sensitive for mAb 12B8 and 6D4 detection. The epitopes, designated as 12B8 and 6D4, were tested for protein tagging. They were appended to the N- or C-terminus of four human proteins, the tumour suppressor protein VHL (von Hippel-Lindau), SUMO4, MHC class-II DQbeta and -DPbeta for expression in mammalian cells. Western detection, immunoprecipitation and localisation of the tagged proteins were successfully demonstrated. Thus, the 12B8 and 6D4 epitope tag can be universally used for the immunodetection of recombinant proteins and to study protein-protein interactions.