HLA-DO is a lysosomal resident which requires association with HLA-DM for efficient intracellular transport.

The murine MHC class II molecule H2-O is expressed in B-cells and in thymic epithelium but the human equivalent, HLA-DO (DO), has not been detected, though the corresponding genes, HLA-DNA and HLA-DOB, are well known. Here we show DO to be a lysosomal resident in B-cells. Surprisingly, DO forms stable complexes with HLA-DM (DM), another lysosomal class II-like molecule which is important for class II-restricted antigen presentation.

In vivo characterization of the proteasome regulator PA28.

A proteasome regulator, termed PA28, has been shown to modulate peptidase activities of the proteasomes in vitro. Two different but homologous PA28 molecules, designated as PA28alpha and PA28beta, have been cloned. Both alpha and beta polypeptides of PA28 are found in PA28 complexes isolated from cells, indicating that both are constituents of functional PA28 complexes.

Molecular mechanism and species specificity of TAP inhibition by herpes simplex virus ICP47.

The immediate early protein ICP47 of herpes simplex virus (HSV) inhibits the transporter for antigen processing (TAP)-mediated translocation of antigen-derived peptides across the endoplasmic reticulum (ER) membrane. This interference prevents assembly of peptides with class I MHC molecules in the ER and ultimately recognition of HSV-infected cells by cytotoxic T-lymphocytes, potentially leading to immune evasion of the virus. Here, we demonstrate that recombinant, purified ICP47 containing a hexahistidine tag inhibits peptide import into microsomes of insect cells expressing human TAP, whereas inhibition of peptide transport by murine TAP was much less effective.