Homozygous and hemizygous deletions within the HLA region determined by interphase FISH.

(A) Schematic representation of the HLA region on chromosome 6p21.3. On the left-hand side, the localization of the microsatellite markers used for LOH and on the right-hand side the 6 PAC/cosmid probes used for interphase FISH. (B-D) Examples of interphase FISH. Each panel represents a composite of 3 to 4 individually captured nuclei, including at least 1 control nucleus without a deletion. In all cases, the red signal is derived from centromere 6, and the green signal is derived from 1 of the 6p21.3-specific probes as indicated on the left. (B) Testicular lymphoma T18 showing homozygous deletions of PACs 93N13 and 172K2 indicated by the presence of 2 centromere 6 signals and no detectable PAC signal. The homozygous deletion was also present in the 20% of nuclei with trisomy 6. (C) Testicular lymphoma T20 showing monosomy 6 and a deletion of PAC 93N13 in 75% of the nuclei with monosomy 6. (D) Testicular lymphoma T25 showing a homozygous deletion of PAC 93N13, including all cells with tetrasomy (25% of cells), and a large hemizygous deletion, including PACs 223H1, 172K2, and cosmid M31A.