B-lymphocytes in CLL and NHL differ in the mRNA splicing pattern of the CD45 molecule

In the present study the cell surface expression of CD45 isoforms on normal and neoplastic human B cells was correlated with splice products of the CD 45 mRNA, using RT-PCR technology. In non-Hodgkin's lymphoma cells in the le ukemic phase (NHL) the majority of the cells expressed a high level of CD45 RA, while in CLL most of the cells expressed a low level. In the Raji and D audi Burkitt B-cell lymphoma lines the main CD45 mRNA product was the large st, unspliced, full-length isoform (456) and the 56 splice product. Similar results were obtained with B-cell lymphoma cells isolated from the periphe ral blood of patients with NHL in the leukemic phase. In EBV-transformed B- cell lines, the 456 and the 56 isoform of CD45 mRNA were predominant, but i n addition a low level of the 5- and 0-exon splice products was detected. A strikingly different pattern was obtained with B-CLL cells. In CLL the lev el of the 456 and the 56 isoforms was low, while that of the 5- and 0-exon splice products was increased. Thus, in contrast to the heterogeneity in th e expression of CD45RO in B-CLL, the majority of the cells contained the CD 45 mRNA splice product coding for CD45RO. Analysis of splice products of th e CD45 mRNA may serve as an additional tool to differentiate CLL from the l eukemic phase of NHL.