Characterization of intracellular HLA-DR, DM and DO profile in K562 and HL-60 leukemic cells

Surface class-II antigen expression fires-up the antigen presentation process and development of immune response. The absence of surface HLA-DR is used in various systems to avoid immune recognition. Most leukemic cells use such mechanism to escape immune surveillance. Here, K562 and HL-60 leukemic cells were examined as to intracellular HLA-DR, -DM and -DO expression, if any. Immunofluorescence scored by UV-microscopy, flow cytometry or confocal microscope analysis detected intracellular pools of HLA-DR, -DO and to a lesser degree HLA-DM, whereas sub-cellular fractionation localized these molecules within endosomes. RT-PCR experiments revealed the presence of HLA-DR alpha beta, HLA-DM alpha beta and HLA-DO beta but not HLA-DO alpha transcripts. Despite the absence of the HLA-DO alpha chain, stable transfectants of K562 with a full length HLA-DO beta-EGFP construct showed that DO beta chain could be translocated to endosomes and form stable complexes with HLA-DR. Such complexes could be responsible for arresting HLA-DR molecules within endosomes, maintaining their surface class-if negative state. (C) 2008 Elsevier Ltd. All rights reserved.