Fig. 8. Specificity of the MHC-PML association. (A-B) MHC-PML association was investigated in the 721.174 B lymphoblastoid cell line (A) and the control B-lymphoblastoid cell line AHB (B) by immuno-FISH on three-dimensionally preserved nuclei. 721.174 cells have only one copy of the short arm of chromosome 6 containing a large deletion of the MHC class II region (from DRA to LMP/TAP). The MHC region was visualised using genomic probes recognising the adjacent DAXX region (red) and PML bodies were detected simultaneously by immunofluorescence (green). (C-D) MHC-PML association was investigated in a derivative of the 721.174 cell line (4D1D10.2), resulting from stable integration of an MHC YAC into chromosome 18. (C) The MHC class II YAC DNA on chromosome 18 was detected using genomic probes recognising the LMP/TAP region (green) and the residual MHC region on chromosome 6 using genomic probes recognising the DAXX region (red). (D) The relative association of PML bodies with each copy of chromosome 18 was determined using a partial chromosome paint (red) to delineate the YAC integration site on band 18q11 and the MHC class II YAC DNA was detected using genomic probes recognising the LMP/TAP region (green). The approximate chromosomal position of these regions is illustrated on the ideograms.