Characterization of two novel pre-B-cell lines (LK63 and LiLa-1): Potential models of pre-B-cell differentiation

Abstract

In this report we describe two newly isolated pre-B acute lymphoblastic leukaemia cell lines. Both cell lines lack EBV as detected by the EBNA-1 gene probed Southern-blots. Neither cell line expressed the B-cell-specific CD20 antigen on the cell membrane. However surface expression of CD20 was induced by phorbol ester (TPA) on both LiLa-1 and LK63 cell lines. Other pre-B and B-cell lines, such as Reh, Nalm-1, and BALL-1 did not exhibit these changes in phenotype. Previous immunoprecipitation studies have noted that a broad 50–55 kD band co-precipitates with the characteristic 33–37 kD CD20 protein. We demonstrate that, while the 33–37 kD CD20 species was undetectable on resting LiLa-1 and LK63 cells, in each case a 50–55 kD protein was immunoprecipitated by the CD20 antibody. However, the failure to detect any cell surface CD20-associated antigen on the control cells by immunophenotyping indicated that the CD20 epitope of the 50–55 kD molecule was not expressed on the cell surface. Following exposure to TPA the 50–55 kD species was reduced over 48–72 h while the level of the p33–37 CD20 protein was increased. Northern-blot analysis showed that the 50–55 kD protein was not a cryptic form of CD20 as the uninduced cells contained no detectable CD20 mRNA. The decrease of the 50–55 kD protein and the acquisition of the mature CD20 molecule were paralleled by a decline in proliferative activity in both cell lines. As expression of CD20 by normal pre-B cells also coincides with the cessation of cell division and maturation towards a mature B-cell phenotype, these cell lines appear to represent models for a discrete stage of B-cell differentiation which may be valuable in defining the signals regulating pre-B-cell proliferation.