Improvements to B cell clonality analysis using PCR amplification of immunoglobulin light chain genes

Aims: Clonality analysis using polymerase chain reaction (PCR) amplification of the immunoglobulin heavy chain (IgH) gene is an important aid to the diagnosis of B cell lymphoproliferative diseases. However, the method has a relatively high false negative rate. In an attempt to improve detection rates simple PCR strategies for clonality analysis of B cell populations using amplification of Ig light chain genes have been developed. Methods: Novel PCR protocols, designed to amplify Igκ and Igλ light chain genes, were evaluated using high molecular weight DNA samples from 28 selected cases of B cell lymphoma with known light chain expression and 12 reactive lymphoid specimens. Products were run on 10% polyacrylamide minigels using heteroduplex analysis. Conventional IgH PCR analysis was also performed. Twelve randomly selected formalin fixed, paraffin wax processed samples from cases submitted for molecular genetic analysis were also studied. Results: Polyclonal products were seen in all reactive lymphoid samples. Using Igκ PCR, 24 of 28 lymphomas, including four of five IgH negative cases, displayed monoclonal patterns. Using Igλ PCR, eight of 12 Igλ expressing tumours, including two of five IgH negative cases, showed monoclonal patterns. Standard IgH PCR demonstrated monoclonality in 23 of 28 B cell lymphomas. The detection rate was improved to 27 of 28 lymphomas using heavy and light chain PCR. Efficient amplification was achieved using paraffin wax processed samples, seven of which showed monoclonality compared with eight using IgH PCR. Conclusions: Ig light chain PCR, used in conjunction with heavy chain analysis, enables improved detection of B cell monoclonality using routine histological specimens and can provide additional clone specific markers for the study of the biology of B cell tumours.