Identification of immunoglobulin lambda isotype gene rearrangements by Southern blot analysis

The human immunoglobulin lambda (Ig(lambda)) gene locus contains seven homologous C(lambda) exons which are organized in a tandem array, each of which is preceded by a single J(lambda) gene segment. The J-C(lambda)1, J-C(lambda)2, J-C(lambda)3, and J-C(lambda)7 are functional gene regions and encode for the four Ig(lambda) isotypes, whereas J-C(lambda)4, J-C(lambda)5, and J-C(lambda)6 are non-functional (pseudo) Ig(lambda) gene regions. Recently, we demonstrated that Southern blot analysis with the IGLC3 probe in combined EcoRI/HindIII digests allows detection of approximately 95% of all clonal Ig(lambda) gene rearrangements in B cell malignancies. Although this single probe/enzyme combination is quite effective in detecting Ig(lambda) gene rearrangements, it should be noted that it results in a complex pattern of multiple germline bands of different density, which needs experience for correct interpretation. To improve further the reliable detection and identification of clonal Ig(lambda) gene rearrangements, we developed a new set of seven 'isotype-specific' DNA probes: the IGLC1D probe for the J-C(lambda)1 gene region, the IGLC2D probe for the J-C(lambda)2 gene region, the IGLJ2 probe for the highly homologous J-C(lambda)2 and J-C(lambda)3 gene regions, and the IGLC4D, IGLJ5, IGLJ6, and IGLJ7 probes for the last four J-C(lambda) gene regions, respectively. In combination with optimally chosen digests (ie HindIII, BglII, BamHI, and/or EcoRI) the seven probes indeed allow easy detection and identification of all rearrangements in the seven J-C(lambda) gene regions. The applicability of the probe/enzyme combinations was confirmed upon analysis of clonal 'Ig(lambda)-isotype' gene rearrangements in 40 B lineage malignancies.