Frequent discordance of the light-chain isotypes expressed by serum monoclonal components and leukaemic B-cells.

ABSTRACT

In B-cell malignancies, it is generally held that the monoclonal components (MC) are produced by the malignant clones. Genetic relatedness implies the concordant expression of light-chain (LC) isotypes in the MC and at the surface of the malignant lymphocytes. We reviewed a series of 91 B-cell leukaemias, immunophenotyped by flow cytometry in our laboratory. A serum MC had been sought in 75 of these patients, and had been found in 23 (31%). Biclonal serum components were detected in three cases. LC concordance could not be assessed in three cases of surface LC-null lymphocytes. Of the 23 MC studied in 20 patients, light-chains were discordant in 39%, mostly due to kappa MC in lambda leukaemias. The origin of LC discordance remains speculative. It could be due to the emergence of subclones with the same primal VDJ gene rearrangement or, alternatively, to the development of new B-cell clones escaping immune surveillance from deregulated T-cells.