Abstract

Aims—To directly visualise immunoglobulin (Ig) heavy (H) and light chain genes (κ and λ) in metaphase chromosomes and interphase nuclei of normal and malignant lymphocytes using small genomic probes targeted to intragenic sequences.

Methods—Cytogenetic preparations from phytohaemagglutinin stimulated lymphocytes, B-chronic lymphocytic leukaemia (B-CLL) cells, and a B-prolymphocytic leukaemia (B-PLL) cell line, containing a t(11;14), were hybridised in situ using biotin or digoxigenin labelled plasmid probes. The κ genes were visualised with a combination of probes for the Cκ, Jκ, Vκ1, and Vκ2 segments, the λ genes with a probe containing the Jλ2-Cλ2, Jλ3-Cλ3 segments and the H genes with a probe for Cλ2. Hybridisation sites were visualised using appropriate fluorochrome conjugates and images were analysed by digital microscopy.

Results—In both normal and malignant lymphoid cells, the κ and λ genes were visualised as a single dot signal, whereas the H λ genes were resolved as either two or three separate signals per chromatid in metaphase chromosomes or per allele in interphase nuclei. In the malignant PLL cells, double hybridisation experiments with a painting library specific for the chromosome 11 showed that the λ region was retained in the translocated chromosome, with an in situ resolution pattern similar to that of the normal allele.

Conclusions—This study shows that a high resolution in situ analysis of the three Ig loci can be efficiently performed with small size genomic probes on both normal and malignant lymphoid cells. Such an approach offers a flexible tool for the molecular characterisations of these loci on chromosomes and individual neoplastic cells.