EXPRESSION OF MDR1 AND MRP IN THE NORMAL B-CELL HOMOLOG OF B-CELL CHRONIC LYMPHOCYTIC-LEUKEMIA

B-cell chronic lymphocytic leukaemia (CLL) cells commonly express the multidrug resistance phenotype. The aim of this study was to establish whether the normal homologue in B-cell ontogeny of B-CLL also express ed the multidrug resistance (mdr) phenotype. Human tonsillar lymphocyt es were sorted to yield two B-cell subsets based on the expression of CD19, CD5 and CD10. The normal homologue was represented by a populati on of B cells that was CD19 positive, CD10 negative and weakly express ed CD5. Based upon functional analysis and the detection of mdr1 mRNA by semi-quantitative PCR, these cells expressed the mdr phenotype. In contrast, functional multidrug resistance could not be demonstrated in CD19-positive CD10-positive cells with strong expression of CD5, nor could mdr1 mRNA be found in these cells. MRP was variably expressed in both B-cell subsets with no discernable differences in the pattern of expression. We conclude that normal B cells with a phenotype resembli ng that of B-CLL cells express the multidrug resistance phenotype.